Diabetic nephropathy is a major microangiopathic complication of diabetes mellitus. Its features are represented by: proteinuria and renal function decrease. The etiology of proteinuria in diabetic patients is assessed in this study. The study was performed on 30 patients with diabetes mellitus (11 type 1, 19 type 2) and proteinuria (19 males and 11 females), at the mean age of 42.1+/-7.72 years. Renal biopsies were done with Vim-Silverman needle, using hematoxylin-eosin and PAS staining. Diabetic retinopathy was found in 26 patients (86.66%). The values of proteinuria were: 0.62+/-0.07 g/24 hours in 4 (13.33%), 2.41+/-1.26 g/24 hours in 10 (33.33%) and 4.68+/-2.11 g/24 hours in 16 patients (53.33%). 18 patients presented elevated blood pressure (170.11+/-6.25/97.12+/-4.44 mmHg). Reduced creatinine clearance (48.01+/-7.25 ml/min) was found in 7 patients (23.33%). Histological analysis showed: diffuse diabetic glomerular lesions in 14 patients (46.66%), nodular diabetic glomerular lesions associated with diffuse glomerular lesions in 12 patients (40%) and membranous glomerulonephritis, without diabetic lesions in 4 patients (13.33%). Appearance of proteinuria in diabetic patients is not synonymous with diabetic nephropathy, requiring further investigations. including renal biopsy.