BACKGROUND: Analysing the evidence generated over decades, the World Health Report 2008 recommended the expansion of primary health care (PHC) to achieve better population health, higher equity and lower costs. Over the last two decades, the Iranian model of PHC has resulted in population health indices that match the best in the region. Despite the extensive PHC networks in rural areas, there was an expansion of private outpatient care and hospital-based services. This model has been inadequate to meet the evolving health needs of the population and increasingly difficult to afford. In response, a family medicine (FM) programme has been implemented since August 2005, funded through Behbar, a model of social insurance. In this paper, we aim to identify facilitators of and barriers to implementation of FM in Iran. METHODS: Data were collected between November 2006 and May 2007 through semi-structured interviews at national (19 interviews), provincial (9) and local (43) levels, and through a purposive document analysis. The framework approach was used for analysing interviews. Document analysis followed a narrative contextual framework. We interpreted data using an interpretive framework consisting of multiple streams and network theories. RESULTS: The introduction of Behbar provided FM advocates with the opportunity to place FM on the policy agenda. They skillfully coupled the two policies and defined FM as the only solution to fulfill Behbar. However, the manner in which policy was formed was the main obstacle to desired FM implementation. CONCLUSION: The interpretive framework links the concept of outreach to the poor and enhancing equity to rationing health services at a particularly opportune moment in Iran. However, using windows of opportunity to implement a major policy change, if it results in sacrifices in planning and preparedness, may harm the policy and the future success in achieving its objectives.