During a 6-year period, 64 patients with a nephrotic syndrome, shown histologically to result from minimal change nephropathy, were studied for a mean of 4.5 years. Fifty of the patients showed no glomerular immunoglobulin on immunofluorescent or immunoperoxidase study, but 14 had mesangial deposits of IgM. The onset characteristics, response to treatment, and long-term course were similar in the two groups. We conclude that IgM deposition in the mesangium in patients with minimal change nephrotic syndrome is of no prognostic value, and our data do not suggest that this group of patients, although a histopathologic entity, represent a clinically distinct group.