BACKGROUND: There are high incidence and mortality rates of breast cancer in Brazil. Brazilian's social and economic disparities, along with complexities of its health system pose challenges to the appropriate implementation of mammography screening as a public policy for the population. In 2015, the Ministry of Health updated the recommendations for the early detection of breast cancer, which had, until then, been based on specialists' consensus, maintaining biennial screening mammography for women aged 50-69 years. However, the screening coverage did not exceed 25% of the expected number of exams for the Brazilian population who use the public health system. The objective of this study was to analyze barriers and facilitators (determinants) of opportunistic mammography screening in the Brazilian public health system. METHODS: We conducted a scoping review to examine the extent to which guidelines have been implemented from 2015 to 2025, excluding those that (1) did not include the population aged 50 to 69 years, (2) did not discuss mammographic screening in the Brazilian public health system, (3) included populations with cancer or at high risk of cancer. Results were coded into the domains of the Consolidated Framework for Implementation Research (CFIR). RESULTS: In the 85 articles selected, we coded 74 determinants, 50 referring to barriers and 24 to facilitators. The barriers were related to the outer setting 18(24.3%), inner setting 11(14.9%), characteristics of individuals 9(12.2%), process 6(8.1%), and intervention characteristics 6(8.1%). The facilitators were related to the outer setting 14(18.9%), inner setting 5(6.8%), intervention characteristics 3(4.1%) and individual characteristics 2(2.7%). CONCLUSION: Using CFIR helps understand the multiple interrelated factors that affect the implementation of opportunistic mammographic screening in the Brazilian public health system. Our results can provide initial data for further studies that aim to improve and organize the implementation of mammography screening in Brazil.