Diabetes, hypertension, and ischemic heart disease are less frequent among physically active subjects. The aim of the present national population-based study was to compare the prevalence of these three diseases between former Finnish elite athletes and referents. The subjects consisted of surviving former male athletes who represented Finland between the years 1920 and 1965 at least once in international competitions and referents who at the age of 20 were classified as completely healthy at a medical examination, and who responded to a questionnaire in 1985 (athletes, n = 1,282; referents n = 777). In 1985, they completed a questionnaire with medical, life-style, and psychosocial items; at that time, the leisure physical activity was greater in previous athletes than in referents. The presence or absence of the three diseases was identified from the questionnaire or from at least one of three registers: Finnish hospital inpatient discharge register, reimbursable medication register, and disability pension register. When compared with referents, both endurance and mixed-sports athletes had lower age-adjusted odds ratios (ORs) for all studied diseases. Compared with referents, power-sports athletes had a higher risk for high body mass index (BMI) but a lower risk for ischemic heart disease. Subjects with high BMI had an increased risk for all three diseases. Smokers had a higher risk for diabetes and ischemic heart disease compared with those who were never smokers. After adjustments for age, BMI, smoking history, and occupational group, compared with referents, former endurance athletes had the lowest ORs for diabetes (OR 0.24; 95% confidence interval, 0.07 to 0.81) and ischemic heart disease (OR 0.33; 0.18 to 0.61).(ABSTRACT TRUNCATED AT 250 WORDS)