It is important to differentiate proteinuria from non-diabetic renal diseases (NDRD) or diabetic nephropathy in diabetic patients. The purpose of our study was to evaluate the prevalence of NDRD. A retrospective analysis was performed on diabetic patients who had undergone renal biopsy during a 6-year period. Our study revealed a high prevalence of NDRD in the diabetic population. Sixty-nine patients were investigated, 52.2% were diagnosed as NDRD and 47.8% as DN. Focal segmental glomerulosclerosis was the most common lesion found in patients with NDRD. We found a relationship between DN and fasting blood glucose level, systolic blood pressure, diastolic blood pressure, LVMI, intima-media thickening (IMT), and the presence of carotid plaques. Patients with NDRD had a lower incidence of diabetic retinopathy (DR). The absence of DR to differentiate NDRD had a sensitivity of 72.7%, a specificity 91.7%, and an ROC=0.822. Fasting blood glucose level had a sensitivity and specificity of 93.9% and 75%, respectively. Similarly, the use of IMT had sensitivity and specificity of 90% and 75.8%, respectively. In this study, we determined that the absence of DR, a lower fasting blood glucose level, and IMT is useful in differentiating NDRD from DN in diabetic patients with overt proteinuria.