OBJECTIVE To study trends over 40 years in cardiovascular risk factors in normal weight, overweight and obese men, all aged 50 when examined. Design. Cross-sectional studies of five successive cohorts of men aged 50. METHODS City of Göteborg, Sweden. METHODS Random population samples of altogether 3251 urban Swedish men born in 1913, 1923, 1933, 1943 and 1953. METHODS Anthropometry, cardiovascular risk factors, rates of nonsmoking, normotension and serum cholesterol <5 mmol L(-1) over four decades. RESULTS Over 40 years, there was a net increase in body mass index (BMI) from 24.8 (SD = 3.2) to 26.4 (3.7) kg m(-2) (P < 0.0001), with an increase in the prevalence of obesity (BMI >or= 30 kg m(-2)) from 6.0% in 1963 to 13.8% in 2003. Favourable trends with respect to smoking, blood pressure and serum cholesterol were observed similarly amongst normal weight, overweight and obese men. In 1963, 24% of obese men were normotensive compared to 45% in 2003, and 6% had serum cholesterol <5 mmol L(-1) compared to 34% in 2003. Compared with obese men in 1963, men who were obese in 2003 had an odds ratio (OR) of 3.39 being a nonsmoker [95% confidence interval (CI): 1.56 to 7.36], 2.67 of being normotensive (1.23 to 5.83) and having serum cholesterol <5 mmol L(-1) of 8.30 (2.37 to 29.0). However, optimal risk factor status - no smoking, normotension and total serum cholesterol <5 mmol L(-1)- was still present in less than one in six men in 2003, similar across BMI categories. CONCLUSIONS Obese Swedish men who are now in their fifties have much lower levels of other risk factors compared with obese men 40 years ago. This could contribute to explain why coronary heart disease death rates still are falling despite increasing rates of obesity.