The World Health Organization’s safe surgery checklist is a useful tool to reduce adverse events in hospitals, but its effective implementation is still a challenge. This study aims to assess adherence to the Checklist in urological and gynecological surgeries in two teaching hospitals in Natal, Rio Grande do Norte, Brazil. The design was observational transversal; elective surgeries were selected, and the collection took place through a review of medical records. Adherence was described based on the existence and quality of filling out the Checklist analysis. Of the 375 surgeries reviewed, 61% had a checklist, and 4% were fully completed. The existence of the Checklist was associated with gynecological surgeries (maternity) (OR = 130.18) and a longer duration of surgery (OR = 2.13), while the quality of filling was associated with urological surgeries (general hospital) (β = 26.36). Adherence to the Checklist needs to be improved, and the differences suggest the influence of the different implementation strategies used in each institution. Check List; Patient safety; Operative Surgical Procedures while the quality of the Checklist was related to urological surgeries (β = 26.36). This study provides information on the process of implementation and adherence to the WHO checklist in hospitals, a subject that has been little explored in the scientific literature in general, especially in the context of developing countries, particularly in Latin America. Its deepening allowed the identification of problems and factors associated with the effective use of the Checklist, useful information to enable the comprehensive incorporation of this technology and achieve the good results in patient safety desired by the WHO Safe General Surgery Instruments Saves Lives campaign7. The use of the Checklist may have promoted good levels of Verification of important aspects for patient safety, such as “patient identification and consent” (item 1: 94.3%) and proof of “allergy” (item 5: 94.3%) before the patient is under anesthesia. Furthermore, some of the best-completed items were precisely those directly related to the risk of death, such as “allergies” (item 5), “difficult airway” (item 6), and “risk of blood loss” (item 7). Studies show that items interpreted as more important or of greater risk to the patient tend to have better adherence by the professional responsible for their verification16, 17. The difficulties in implementing the Checklist observed in this research are greater than those reported by other authors, in relation to both the existence of the instrument (60.5% found in the present investigation versus 83.3%, 96.9% and 92% in studies in Spain, England, and Canada, respectively), regarding its complete completion (3.5% in this survey versus 27.8% in the Spanish)10, 13, 18. It was observed that the greatest number of errors is present in the moments “before anesthetic induction” and “before the surgical incision,” with items 2 and 3 (“demarcated surgical site” and “anesthetic safety check”) negatively influencing the moment 1, and items 10, 11 and 14 (“critical events of the surgeon,” “critical events of the anesthesiologist” and “imaging exams”) compromising moment 2. Failure to complete these items may be a priority object of investigation for interventions timely. As for the demarcation of the surgical site, its importance is evidenced by the notification of one in fifty thousand to one hundred thousand procedures in the wrong place in the United States, equivalent to 1,500 to 2,500 incidents per year7. In Brazil, there is no explicit notification system that provides data for comparisons. Regarding the Verification of anesthetic safety, failure in its evaluation can result in higher mortality rates, reaching, in some regions of the world, rates of up to one death in 150 patients who receive general anesthesia. Anesthetic complications are among the main causes of mortality before and during surgery, with most errors (65%) occurring during anesthetic induction19, 20. Regarding the factors associated with adherence, although some variables stood out in the bivariate analysis, most of them lost relevance when considered together in the multivariate model. The care center variable showed statistical significance for the existence of a checklist and for the percentage of filled items, highlighting the importance of a careful analysis of the context in which the instrument was implemented in each institution. The variable duration significantly influenced the existence of a checklist, as longer surgeries cover a greater number of critical steps, which could justify a greater concern on the part of the team in using it. Cullies et al.21evaluated 80 checklists before the patient left the room and 81 before anesthetic induction with adherence rates lower than expected. However, in higher-risk surgeries, adherence was higher. The analysis of adherence by care center and the assessment of the context of each one of them pointed out some differences, such as the person responsible for applying the Checklist, a nursing technician in the maternity hospital and a resident physician in the general hospital, and the different surgical specialties in each center. We believe that the differences regarding the existence of the Checklist and the quality of its completion may mainly reflect the different implementation strategies used. Carney et al.22suggests that individual perceptions among members of the surgical team about the importance of each item on the Checklist directly influence its implementation. According to Conley et al.23, a new instrument must not only be implemented; it must be explained to the team at the time of implementation why and how it should be used. In this regard, it is interesting to note that, in the maternity ward, the decision of the hospital management to use the Checklist in a systematic way positively influenced its greater use, but the educational actions were not enough to qualify the staff of that institution, resulting in lower quality of filling. On the other hand, in the general hospital, the voluntary and negotiated implementation of the tool by a multidisciplinary team resulted in its better use, despite the low adherence. We believe that this result may be an indication of the need to combine different strategies to ensure effective implementation, including the establishment of norms or policies promoted by the management, as well as the negotiation and empowerment of the surgical teams. The adherence identified in both hospitals reflects the barriers present in the organization of the participating institutions. Safe practices are better implemented when there are leadership structures and systems aimed at this goal, enabling implementation environments based on the 4 As theory ( awareness, accountability, ability [enabling], action [action] )24. The two hospitals in question do not have a service quality management program or a patient safety committee; moreover, risk management still does not focus on this type of security incident. By putting the 4 As theory into practice, sensitization makes it possible to overcome the cultural barrier to the application of the Checklist; accountability determines which professional will apply it and which clinical or management leaders will be accountable for its implementation; the qualification allows to adequately prepare the team for effective action; finally, the action must involve cycles of evaluation and continuous improvement of the adherence and effectiveness of the Checklist. There are also no clear interventions to assess and promote an organizational culture of valuing safety, which may have made it difficult for the teams to perceive the relevance of the Checklist and a positive attitude. Improving security requires understanding the science of error, considering human factors and system failures, with investment in training to mitigate potential errors and even avoid them25. On the other hand, although external initiatives are still incipient in our country, there are perspectives of strengthening them, given the recent institution of the National Patient Safety Program (PNSP) by the Ministry of Health of Brazil. The general objective of this program is to contribute to the qualification of health care in all health establishments in the national territory and presents, among its competencies, a proposal for safe protocols for surgical and anesthetic procedures26. As for the limitations of this study, it is highlighted that the analysis was restricted to the specialties of gynecology and urology, with the data based on filling out the Checklist and not on direct observation of this action; in addition, the research instrument of one of the assistance centers was modified in relation to that recommended by the WHO. This last factor hindered the complete completion of the tool due to the absence of the items “demarcated surgical site” (item 2) and “anesthetic safety check” (item 3) in the Checklist of motherhood. We warn that this weakness in the implementation may be repeated in other places due to the management team’s interpretation of the adaptations to its reality. A study that addresses the use of the Checklist in gynecology treats the marking of the surgical site as being usually unnecessary; however, WHO encourages the inclusion, in the instrument, of essential items for each service, but not the exclusion of items already recommended27. Singh et al.28 reinforce this premise in obstetric and gynecological surgeries. Since the results refer to two teaching hospitals, caution should be exercised when extrapolating to other hospitals, national or international, as both adherence and associated factors may vary according to different contexts. Future studies can quantify other variables possibly related to adherence to explain the variability more comprehensively in implementation success. Despite the limitations, it is believed that this research can help to understand the challenges of the checklist implementation process in hospitals in other regions of the country, whose barriers are similar. The indispensable need to comply with the guidelines of the WHO implementation manual and devote time to the training of surgical teams is highlighted, highlighting the relevance of the new technology, as well as the qualification for its use, through practical sessions and study-pilot to identify usage difficulties. Among the proposals, it is suggested that institutions invest in organizational capacity to promote actions in safety, as only with structures and leadership systems geared towards this end activities will have the necessary solidity and continuity. In addition, external support and regulation initiatives can promote awareness and accountability, including through criteria provided for in management contracts. It is also recommended feedback to the surgical teams, as well as the use of indicators of the effectiveness of the Checklist in reducing complications, aiming to increase awareness through local evidence of its positive impact. Conclusion The low adherence to the Checklist observed in the hospitals evaluated in this study possibly reflects on the occurrence of adverse events in surgery, such as hospital stay, risk of readmission, need for intensive care, mortality, and others, to be confirmed in future studies. There is ample scope for improving adherence to the WHO safe surgery checklist in the hospitals studied, requiring a more structured implementation in order to ensure its proper use while also ensuring the quality and safety of patient care. The differences in the use of the Checklist and the quality of its completion in the hospitals evaluated suggest the importance of combining different implementation strategies, characterized both by regulation as well as by the awareness and empowerment of the surgical teams.