Diabetic glomerulosclerosis is the most frequent cause of renal disease in patients with type II diabetes mellitus (DM), sometimes accompanied by vascular lesions. However, other glomerular pathologies are important in these patients. The aim of this study was to evaluate the prevalence of non-diabetic nephropathy (NDN) in selected patients with type II DM, and to identify clinical markers that may predict its presence in this population. We reviewed 20 renal biopsies performed on twenty patients with type II DM. Nine of them showed diabetic nephropathy (DN) (45%), whereas eleven showed NDN (55%): 1 IgA nephropathy, 3 vasculitis and 7 membranous nephropathy. We found no differences between the two groups with regard to sex, duration of DM, insulin therapy, glycosylated haemoglobin, proteinuria, presence of nephrotic syndrome, hypertension, serum IgA level or renal size. The NDN group had haematuria in 63.6%, whereas the patients with NDN had it in 44.4% (NS). Body mass index was higher in NDN patients (30 +/- 6.7 vs 22 +/- 2.9; p < 0.01), The same was true for creatinine clearance (82.2 +/- 51.4 ml/m vs 40.4 +/- 19.6 ml/m; p < 0.05). The age at the moment of diagnosis was higher in ND patients (67 +/- 11.2 vs 54.3 +/- 4.6; p < 0.05). The 3 patients who had diabetic retinopathy were found to have DN on renal biopsy (diagnostic specificity = 100%), although 66.7% of the patients with diabetic glomerulopathy had no retinopathy. We conclude that patients with type II DM with renal findings suggesting non-diabetic renal disease frequently it have NDN, and a renal biopsy must be performed. The presence of retinopathy has a predictive value of 100% in predicting DN, therefore its existence may make this diagnostic procedure unneccesary.