Proteinuria was estimated in 600 non-insulin dependent diabetes mellitus (NIDDM) patients in 24 hrs collection of urine. The test was repeated at least twice in a year to confirm the persistence of proteinuria. Mild proteinuria (200-500 mg/d) occurred in 94 (15.7%) and nephropathy (> 500 mg/d) in 112 (18.7%) patients. Nephropathy commonly occurred with long-standing diabetes (> 10 years). Development of proteinuria correlated directly with the duration of diabetes, diastolic and systolic blood pressure, age of the patients, serum creatinine and inversely with creatinine clearance. Retinopathy was seen in 75% of those with nephropathy. It is concluded that proteinuria occurs in one third of NIDDM patients and the risk of nephropathy increases with duration of disease.