The primary glomerular disease in patients with diabetes mellitus is rare. Several reports have shown that primary glomerular diseases can be superimposed on diabetic nephropathy. The recognition of nondiabetic glomerular diseases in diabetic patients is of utmost importance since they might be successfully treated. This would positively affect the otherwise poor prognosis of renal disease in diabetic patients. The suspicion on nondiabetic renal disease is raised by the appearance of urinary abnormalities such as hematuria, massive nephrotic proteinuria or deterioration in renal function in patients with diabetes mellitus but without coexisting diabetic retinopathy. We report on diabetic patients who underwent renal biopsy because of the massive nephrotic proteinuria and non-nephrotic proteinuria without diabetic retinopathy, hematuria, and because of the deterioration of renal function. On pathohistological examination different types of primary glomerular diseases were found. The diagnosis and the treatement of glomerular diseases improved the renal prognosis in some of these patients.