STUDY OBJECTIVE--To assess changes in the body mass index (BMI, weight (kg)/height2 (m2) and in the prevalence of obesity in Swedish men during the 1980s. DESIGN--Data from two successive cross sectional surveys were used. SETTING--The whole of Sweden. PARTICIPANTS--Subjects included in the analyses were 7055 men from a 1980-81 survey (response rate 83.4%) and 6081 men from a 1988-89 survey (response rate 79%). Men were aged 16-84 years and were a representative sample of Swedish males. MEASUREMENTS AND MAIN RESULTS--The results were based on self reported weight and height obtained during interview. After adjustment for sociodemographic variables, a significant increase in the mean BMI of the entire population of men was found between 1980-81 and 1988-89 (0.23 kg/m2; p < 0.001), with a particularly large increase in the 25-34 year age group (0.45 kg/m2; p < 0.0001) which corresponds to 1.4 kg for a man 180 cm tall). In manual workers this value was 0.25 kg/m2 (p < 0.0005). This increase was also reflected by a significant relative increase in the prevalence of the combination of overweight and obesity (BMI > 25 kg/m2) of about 19% (odds ratio = 1.19, 95% confidence intervals: 1.09, 1.29). CONCLUSIONS--During the 1980s the mean BMI and the prevalence of overweight and obesity among adult Swedish men increased.