Criteria for renal biopsy in proteinuric type 2 diabetes mellitus (T2DM) patients have been not defined. Usually criteria for renal biopsy in type 1 diabetes mellitus (T1DM) are used (microhaematuria, absence of diabetic retinopathy (DR), uncharacteristic change in renal function or immunological abnormalities). The aim of this study was to reconsider the indications for renal biopsy in T2DM using T1DM criteria, to determine whether they are useful in identifying patients with potentially treatable lesions. We studied 127 proteinuric patients with T2DM. Renal biopsy was performed in 35 who met the criteria for biopsy. Biopsy revealed diabetic glomerulopathy (DG) in 29 (83%) (in three associated with nondiabetic renal disease), immunoglobulin A (IgA) glomerulonephritis in three, focal glomerulosclerosis in one and normal glomeruli in two. DG was diagnosed in 17 (74%) of the patients without DR, in 18 (78%) of the patients with microhaematuria and in 10 (67%) of the patients with microhaematuria and without DR. All patients with DR had DG alone, except three with sudden unexpected changes in renal function. We conclude that DG is the most commonly found renal lesion in T2DM patients with proteinuria biopsied according to T1DM criteria, even in patients with microhaematuria or without retinopathy. Thus, these biopsy criteria are not useful in identifying patients with potentially treatable other renal diseases.