The potential health gains from active lifestyles are very well-known and it is recommended that all adults dedicate at least 30 minutes to activities of at least moderate intensity at least five days a week. What is still not known is how to help sedentary people follow this recommendation, by means of brief interventions feasible in routine general practice. This multi-center study was designed to evaluate the effectiveness of a physical activity promotion program (called PEPAF) implemented in 56 general practices of the Spanish public primary health care system. The study will test the capacity of the program to increase the physical activity level, physical fitness and health related quality of life of sedentary people.