Previous studies have shown that the angiotensin-converting enzyme (ACE) gene polymorphism is associated with an increased risk of vascular disease in non-diabetic patients. The present study was conducted on 509 NIDDM patients who underwent a screening test to determine their ACE genotype for the Appropriate Blood Pressure Control in Diabetes (ABCD) Trial. Various baseline indices were correlated with the three ACE polymorphisms. The genotype was determined through polymerase chain reaction amplification of the angiotensin-converting enzyme polymorphism. The univariate relationship between the presence of the DD genotype with nephropathy as measured by urinary albumin excretion (UAE), and a history coronary artery disease (CAD) was then examined. Finally, a multiple model for each UAE and CAD was created so as to determine the independent effects of the presence of the DD genotype on each diabetic complication. Univariately, the presence of the DD genotype was associated with diabetic nephropathy. Furthermore, in a multiple model predicting diabetic nephropathy, the presence of the DD genotype was independently associated with diabetic nephropathy (odds ratio = 2.8, 95% confidence interval 1.4 to 5.5) but not CAD. Thus, the ACE DD genotype in 509 non-Hispanic white NIDDM patients in a metropolitan area in the U.S. was independently associated with the presence of diabetic nephropathy and, therefore, may be potentially used as a marker for NIDDM patients at risk for developing diabetic nephropathy.