OBJECTIVE: We aimed to evaluate the effect of leisure time physical activity on blood lipid levels, in a random sample of cardiovascular disease-free individuals from the Attica basin. DESIGN AND METHODS: The ATTICA study is a population-based cohort, which during 2001-2002 randomly enrolled 2772 men (n = 1376, 45 +/- 12 years old) and women (n = 1396, 45 +/- 13 years old). Physical activity status was evaluated through intensity (kcal/min expended per day), frequency (per week) and duration (min). Multivariate data analysis evaluated the association of blood lipids with physical activity levels. RESULTS: 578 (42%) men and 584 (40%) women were physically active. Compared to sedentary women, physically active women had lower levels of total cholesterol (P < 0.05), low-density lipoprotein (LDL) (P < 0.05), oxidized LDL-cholesterol (P < 0.05), triglycerides (P < 0.05) and apolipoprotein B (P < 0.05) and higher levels of high-density lipoprotein (HDL)-cholesterol (P < 0.05) and apolipoprotein A1 (P < 0.05). Similar associations were observed in men, but they did not reach statistical significance. However, after adjustments for age, smoking habits, body mass index and dietary intake were made, the effect of physical activity on blood lipids remained statistically significant only for HDL-cholesterol (P < 0.05) and apolipoprotein A1 (P < 0.05) levels in women. Moreover, physical activity was associated with lower total cholesterol levels both in nonsmoker men (-7%, P = 0.032) and nonsmoker women (-2%, P = 0.064) and lower triglyceride levels in nonsmoker men (-15%, P = 0.086) and nonsmoker women (-9%, P = 0.036). CONCLUSIONS: Although almost all blood lipids were inversely associated with physical activity status, only HDL-cholesterol and apolipoprotein A1 concentrations were significantly affected by exercise in women.