A retrospective study was done on 66 diabetic patients who had renal biopsies performed during 1979–1994. This review shows 10 patients who presented IgA nephropathy associated with diabetic nephropathy. Six patients had insulin-dependent diabetes mellitus and 4 patients non-insulin-dependent diabetes mellitus. All patients presented with proteinuria and 7 had hematuria. Four patients presented with renal impairment. Histologic evaluation disclosed the presence of thickened glomerular basement membranes and increased mesangial matrix in all cases, associated with nodular sclerosis in 8 cases. By immunofluorescence, diffuse mesangial IgA deposits were observed in all cases. The high incidence of the coexistence of IgA nephropathy and diabetes seems not merely coincidental. Structural and/or functional abnormalities of the glomerular basement membranes might facilitate the development of immune complex glomerular diseases. In patients with diabetes, the appearance of urinary abnormalities and/or deterioration in renal function altered the clinical history of diabetic nephropathy. The disorders are clinically suggestive of the presence of nondiabetic renal disease and raised the possibility of another pathogenetic mechanism.