Most transition countries in Central and Eastern Europe and Central Asia are engaged in health reform initiatives aimed at introducing primary health care (PHC) centred on family medicine to enhance performance of their health systems. But, in these countries the introduction of PHC reforms has been particularly challenging; while some have managed to introduce pilots, many have failed to these scale up. Using an innovation lens, we examine the introduction and diffusion of family-medicine-centred PHC reforms in Bosnia and Herzegovina (BiH), which experienced bitter ethnic conflicts that destroyed much of the health systems infrastructure. The study was conducted in 2004-05 over a 18-month period and involved both qualitative and quantitative methods of inquiry. In this study we report the findings of the qualitative research, which involved in-depth interviews in three stages with key informants that were purposively sampled. In our research, we applied a proprietary analytical framework which enables simultaneous and holistic analysis of the context, the innovation, the adopters and the interactions between them over time. While many transition countries have struggled with the introduction of family-medicine-centred PHC reforms, in spite of considerable resource constraints and a challenging post-war context, within a few years, BiH has managed to scale up multifaceted reforms to cover over 25% of the country. Our analysis reveals a complex setting and bidirectional interaction between the innovation, adopters and the context, which have collectively influenced the diffusion process. Family-medicine-centred PHC reform is a complex innovation-involving organizational, financial, clinical and relational changes-within a complex adaptive system. An important factor influencing the adoption of this complex innovation in BiH was the perceived benefits of the innovation: benefits which accrue to the users, family physicians, nurses and policy makers. In the case of BiH, policies or the innovation are not simply disseminated, but rather assimilated into the health system. The assimilation and implementation of the new PHC model relied on the consensus of a diverse group of adopters; the changes brought by the reforms were aligned with the expectations of the adopters: this created a 'receptive context' for adoption and diffusion of the innovation. The new family-medicine-centred PHC service model had a major impact on professional identity, inter-professional relationships and organizational routines. The post-conflict context was perceived as an opportunity to introduce the new model and implement transformational change, while the complex government structure meant the process of diffusion was as important as the innovation itself. In BiH, a holistic approach-comprising multifaceted and simultaneous interventions at multiple levels of the health system-reduced 'policy resistance' and enhanced the adoption and diffusion of the PHC reforms.