The authors describe a 1-year-old boy who was diagnosed with neuroblastoma by mass screening at age 6 months. The tumor originated from the left retroperitoneum and extended over the midline, involving major vessels and invading the spine with compression of the spinal cord. Although seven courses of chemotherapy consisting of vincristine sulfate, cyclophosphamide, pirarubicin hydrochloride, and cisplatin were administered, there was no reduction in tumor size or decrease in tumor markers. The patient received irinotecan 180 mg/m per day for 3 days. Approximately 3 weeks later the tumor had regressed remarkably, and tumor markers normalized after the second course of irinotecan. This therapy was given a total of four courses every 4 weeks, with the tumor shrinking successively in each session. Four years after treatment there is no sign of recurrence and the patient is doing well. This case may be the first report showing the dramatic efficacy of irinotecan in the treatment of chemoresistant neuroblastoma without the use of other antitumor agents. Irinotecan might be a promising drug in the management of patients with high-risk neuroblastoma.