Background: Pharmaceutical care services have been recognized as the most highly regarded professional pharmacy practice model that allows the identification, intervention, and resolution of drug related problems. This practice provides significant clinical outcomes and can reduce direct and indirect costs for health systems. However, its implementation can be complex and challenging, needing study experiences that aims at overcoming obstacles, especially in free and universal healthcare systems. The objective of this study is to evaluate the implementation of Ambulatory Care Pharmacy services for older adults at Paulista Institute of Geriatrics and Gerontology (IPGG), which is recognized in the city of São Paulo for offering pharmaceutical care services for over 10 years continuously. This initiative and process is independent of external academic interventions or educational institutions. It is hoped that the results may also contribute to advancing the implementation of pharmaceutical care service in similar health systems. Design: This is a case study using multiple sources of data. Qualitative and quantitative data were collected from institutional documents, by participant observation and interviews. Initial themes were identified by content analysis and analyzed under the context-mechanism-outcome configurations (CMO Configurations) in realistic evaluation. Setting: Geriatrics and Gerontology Institute of São Paulo (known as IPGG). Participants: Eleven health professionals and three pharmaceutical care service users.Results: Three CMO configurations were identified and accepted: "Scenario Construction mediated by educational processes", "Contribution to complex needs resolution", and "Organizational Visibility". The CMO (Context-Mechanism-Outcomes) configuration "Logistic activities discourage clinical pharmaceutical services implantation" was denied due to the influence of accepted CMOs. Conclusions: Educational processes which value transdisciplinary knowledge exchanges provide resources required to overcome important obstacles present during pharmaceutical care implementation. Thus, providing and seeking knowledge to build and offer context-consistent clinical health services as well as fulfilling organizational environment requirements can be the key to implement pharmaceutical care service.