Strengthening primary health care (PHC) is considered a priority for efficient and responsive health systems, but empirical evidence from low- and middle-income countries is limited. The stepwise introduction of family medicine across all 81 provinces of Turkey (a middle-income country) between 2005 and 2010, aimed at PHC strengthening, presents a natural experiment for assessing the effect of family medicine on health service utilization and user satisfaction.The effect of health system reforms, that introduced family medicine, on utilization was assessed using longitudinal, province-level data for 12 years and multivariate regression models adjusting for supply-side variables, demographics, socio-economic development and underlying yearly trends. User satisfaction with primary and secondary care services was explored using data from annual Life Satisfaction Surveys. Trends in preferred first point of contact (primary vs secondary, public vs. private), reason for choice and health services issues, were described and stratified by patient characteristics, provider type, and rural/urban settings.Between 2002 and 2013, the average number of PHC consultations increased from 1.75 to 2.83 per person per year. In multivariate models, family medicine introduction was associated with an increase of 0.37 PHC consultations per person (P < 0.001), and slower annual growth in PHC and secondary care consultations. Following family medicine introduction, the growth of PHC and secondary care consultations per person was 0.08 and 0.30, respectively, a year. PHC increased as preferred provider by 9.5% over 7 years with the reasons of proximity and service satisfaction, which increased by 14.9% and 11.8%, respectively. Reporting of poor facility hygiene, difficulty getting an appointment, poor physician behaviour and high costs of health care all declined (P < 0.001) in PHC settings, but remained higher among urban, low-income and working-age populations.