A randomized study was conducted to determine the effect of cyclophosphamide on the rate of recurrence and metastases in children with localized and regional neuroblastoma. One hundred and thirty-four patients were entered and 113 were suitable for analysis. All patients had surgical resection of the primary tumor when possible, postoperative irradiation to the tumor bed when indicated for gross residual disease, and 49/113 received cyclophosphamide, 10 mg/kg/day orally for 7-10 days every 28 days for 1 year. A difference was found in the rate of metastases between the patients who did and did not receive chemotherapy; the overall survival of about 80% in both groups was better than anticipated. All relapses occurred during the first year; there were none in 27 Stage I patients, 8/52 in Stage II and 13/34 in Stage III. Toxicity was minimal, with only two patients developing hemorrhagic cystitis that prevented continued therapy.