Evidence for an association between general obesity and risk of stroke is weak. However, abdominal obesity may be more closely related to stroke risk. The association of body mass index and abdominal obesity (waist/hip ratio) with stroke incidence was examined in 28,643 US male health professionals, aged 40-75 years in 1986, who had no history of cardiovascular disease or stroke. In 5 years of follow-up, there were 118 cases of stroke, of which 80 were ischemic. Compared with men in the lowest quintile of body mass index, men in the highest quintile had an age-adjusted relative risk of stroke of 1.29 (95% confidence interval 0.73-2.27). In contrast, the age-adjusted relative risk for extreme quintiles of waist/hip ratio was 2.33 (95% confidence interval 1.25-4.37). This relative risk was not substantially altered in a multivariate model including body mass index, height, and other potential risk factors. There was a weaker relation with waist circumference alone, with men in the highest quintile (> 40.2 inches) having a relative risk of 1.52 (95% confidence interval 0.82-2.82) compared with men in the lowest quintile (< or = 34.5 inches) (1 inch = 2.54 cm). The results suggest that abdominal obesity, but not elevated body mass index, predicts risk of stroke in men.