Thirty-five consecutive patients with renal biopsy appearances of idiopathic membranous nephropathy, who were initially studied between 1960 and 1969, were reevaluated in 1979 to determine (a) the long-term outcome of idiopathic membranous nephropathy, and (b) whether any clinical or biopsy features at onset would permit prediction of long-term outcome. After fifteen years, actuarial analysis showed that approximately half the patients would be in remission; the rest dead or on dialysis/transplantation programs. Entry into renal failure, in those who ran this course, started at three years after diagnosis and continued steadily for at least another ten years. Likewise, remission was seen as early as one year from onset, but patients were still going into remission after thirteen years of proteinuria. No feature in the glomeruli predicted outcome, but interstitial and vascular changes were seen more frequently in those whose disease persisted or worsened. No onset feature predicted a poor outcome reliably, but younger patients did better than older, and all three children with initial macroscopic hematuria went into remission.