The association between alcohol consumption and the risk of diabetes in Japanese with a low-body mass index (BMI) (< or = 22.0 kg/m(2)), middle-BMI (22.1-24.9 kg/m(2)) and high-BMI (> or =25.0 kg/m(2)) was investigated among a cohort of 5,636 employees of a Japanese insurance company. Participants were free of diabetes at baseline and were followed up for a mean of 5.7 years with annual assessments of fasting plasma glucose (FPG). The outcome was a clinical diagnosis of diabetes on the basis of a questionnaire administered at each follow-up assessment or a follow-up FPG level of 7.8 mmol/l or more. Relative risks and 95% confidence intervals (95% CIs) were estimated by fitting pooled logistic regression models, which included age, gender, BMI, baseline FPG level, current tobacco use and current alcohol consumption. A total of 264 outcome events were recorded. The relative risk of diabetes associated with current alcohol consumption was 3.19 (95% CI 1.09-9.37) among low-BMI individuals, 0.41 (0.23-0.73) among middle-BMI individuals and 0.74 (0.44-1.25) among high-BMI individuals. In this study, current alcohol consumption was associated with an increased risk of diabetes among low-BMI individuals and a decreased risk of diabetes among middle-BMI individuals. A tendency for an association of alcohol consumption with a decreased risk of diabetes among high-BMI individuals was noted, although without statistical significance.