Ten hospitals participated in a cross-sectional study to determine the prevalence of vascular complications in noninsulin dependent diabetes mellitus (NIDDM). The patients were 1433 females and 627 males, aged 24-88 years (mean +/- S.D. = 58.0 +/- 9.9). Duration of diabetes varied from newly diagnosed to 42 years (mean +/- S.D. = 8.2 +/- 6.5). Obesity was noted in 16.9% of males and 27.4% of females. The prevalence of hypertension, myocardial infarction (MI), hemiplegia, absent dorsalis pedis pulse, gangrene and amputation were 38.4, 2.8, 3.7, 5.8, 0.3 and 1.3%, respectively. Diabetic retinopathy (DR) was found in 32.1% of the patients. Proteinuria of greater than or equal to 2+ was observed in 18.7% of the patients. Stepwise multiple logistic regression analysis revealed that hypertension was significantly and independently correlated with MI, hemiplegia and DR but not with proteinuria or absent dorsalis pedis pulse. DR and proteinuria had a strong correlation with each other. Age of the patients weakly correlated with macrovascular diseases. Diabetic control and duration showed a weak correlation with microvascular complications. This study showed that DR was frequently found in Thai NIDDM. Hypertension was not only the commonest disorder but it also showed an independent association with other vascular complications. Early detection and intervention for both need to be emphasized and re-enforced in clinical practice.