5174 Japanese male workers were studied cross-sectionally to examine a possible relationship between obesity and the prevalence of proteinuria (1 + or greater), determined using a reagent strip. The subjects were divided into three groups with body-mass indexes (BMIs) of < 23, 23-24.9 and > or = 25, and the prevalence of proteinuria was compared among the three groups, after adjustments for age, blood pressure and blood levels of HbA1c. Among subjects with hypertension and/or a high level of HbA1c, i.e., > or = 5.9%, the group with a BMI of > or = 25 had a higher prevalence of proteinuria than the group with a BMI of < 23. In contrast, the prevalence of proteinuria was not affected by obesity in the subjects with neither hypertension nor a high level of HbA1c. These results suggest that for obese men with hypertension or diabetes, reducing body weight is important not only as part of the treatment for those diseases, but also to prevent proteinuria.