188 patients with type I MPGN were followed from 1957 to 1975. At last examination, 53% of patients with pure MPGN and 66% of those with lobular MPGN had renal insufficiency; 28 other patients showed clinical improvement and 13 of these had permanent complete remission. In all of these 13 cases, (10 pure MPGN and 3 lobular forms), the clinical remission was spontaneous and occurred 2 to 16 years after the apparent onset. At the time of the first renal biopsy, 7 of these patients had a nephrotic syndrome, 2 had hypertension and 1 had renal failure. A second biopsy was obtained in 5 patients during the clinical remission period and showed in all cases a clear regression of the glomerular lesions. The possibility of spontaneous permanent clinical remission in MPGN should be considered in the indications and methods of treatment and the interpretation of their results.