In 51 patients with type 1 and 9 patients with type 2 membranoproliferative glomerulonephritis, we found a male predominance in both types, a wide age range but with younger patients having predominantly type 2 disease, and clinical presentations that varied and included the nephrotic syndrome, an abnormal urinalysis only, acute nephritis, and recurrent hematuria. Hypertension and impaired renal function at the time of first evaluation, which were present in more than one-third of the patients, presaged a poor prognosis; in most of these patients end-stage renal failure or worsening of renal function occurred. Acute nephritis at onset was also related to a deteriorating course and was especially frequent in patients with type 2 membranoproliferative glomerulonephritis. Retrospective analysis of treatment regimens, in which patients were given an average of 1 year of therapy with prednisone alone or combined with cytotoxic agents, showed no effect in patients who had progressive forms of the glomerulopathy.