The incidence of end-stage renal disease due to diabetes mellitus (DM) is increasing. There have been too few epidemiological studies of the predictors of DM nephropathy, particularly type 2 DM, among a statistically significant population. We studied the prevalence and correlates of DM in a screened cohort in Okinawa, Japan. A total of 9,914 screenees (6,163 men and 3,751 women) over 18 years of age underwent a 1-day health check at the Okinawa General Health Maintenance Association between April 1997 and March 1998. Subjects were considered to have DM if they showed a fasting plasma glucose > or = 126 mg/dl and hemoglobin A1c > or = 7.0%, or if they were receiving treatment for DM. Non-DM subjects were followed-up until March 2000 to see whether or not they developed DM. Relative risk for developing DM was evaluated by Cox proportional hazard analysis after adjusting for confounding variables. A total of 673 screenees (520 men and 153 women) were diagnosed with DM. The prevalence of DM was 67.9 per 1,000 screenees (84.4 for men and 40.8 for women). A total of 7,125 non-DM screenees were examined a second time. Among them, 164 screenees (130 men and 34 women) had developed DM during the follow-up period. Over 2 years, the cumulative incidence of DM was 2.3% (2.9% in men and 1.3% in women). The adjusted relative risk (95% confidence interval) for developing DM was highest for proteinuria, or 1.90 (1.14-3.17). The results indicated that the prevalence and incidence of DM were high among this screened cohort in Okinawa, Japan. Subjects with proteinuria may thus be at high risk for developing DM.