Seven French Medical Centers were involved in a cooperative study evaluating [131I]Metaidobenzylguanidine (131I-MIBG) therapy in advanced neuroblastoma. Children (median age 4 years) had initially a stage III (4 patients) or stage IV (22 patients) neuroblastoma. Before MIBG treatment, 14 patients had a primarily refractory disease, 10 patients were relapsing; in 8 cases, autologous bone marrow transplantation had been performed. Tumour sites were in 24 patients: 13/24 local disease, 8/24 bone metastases, and 7 bone marrow involvement. Catecholamines were elevated in 7/24 patients. The median activity of 131I-MIBG per injection ranged from 30 to 108 mCi; the number of injections varied from 1 to 5. We observed 5/10 pain palliations and 10/24 stabilizations of the disease course for 1 to 7 months with no objective volume tumour response. Haematologic toxicity caused a platelet count less than 150,000/microL in 4 patients, less than 100,000 in 1 patient and less than 50,000 in 7 patients.