31 patients with systemic lupus erythematosus had renal biopsies performed and were followed for up to 14 years. The biopsies were examined by light and electron microscopy. A good correlation was found between the number of electron dense deposits and the progression of renal disease. Patients with massive deposits had poorer prognosis than those with few deposits. Segmental glomerular lesions were usually associated with few deposits. Localization was also important: pure mesangial deposits indicated favorable prognosis, while subendothelial deposits had the opposite effect.