Rate of response to a corticosteroid and frequency of relapse were studied in 33 patients with adult-onset minimal change nephrotic syndrome (MCNS). Of these, 28 patients were treated with oral prednisolone (PSL) at 1 mg/kg/d for from 4 to 8 weeks depending on their response, followed by PSL, at gradually tapering doses for 1 year. Five severely nephrotic patients received 1 g of methylprednisolone intravenously (IV) for 3 days, followed by 40 mg/d oral PSL for 4 to 8 weeks and finally PSL in gradually reduced doses. Sixteen patients (48%) were free of proteinuria within 4 weeks, and 25 (76%) within 8 weeks. Two patients required cyclophosphamide for induction of remission. Age at presentation was not significantly correlated with response time to corticosteroid therapy. Thirty-two (97%) went into remission, and relapse occurred in 11 (34%) of these. As assessed by the life-table method, 84% of patients were still in remission at 6 months after induction of remission, 75% after 1 year, and 63% during the follow-up period (mean, 47.1 +/- 29.1 months; range, 6 to 123 months). Incidence of relapse was not correlated with remission induction time, ie, earlier (less than or equal to 4 weeks) or later (greater than 4 weeks), but was greater in younger (less than 30 years of age) patients than older (greater than or equal to 30 years) patients (P less than 0.03). At the last follow-up, 31 patients (94%) were in complete remission and had normal renal function.(ABSTRACT TRUNCATED AT 250 WORDS)