[131I]Metaiodobenzylguanidine (131I-MIBG) is used for diagnostic scintigraphy and targeted therapy in a range of neural crest tumors, which exhibit an active uptake-1 mechanism at the cell membrane and cytoplasmatic storage in neurosecretory granules. A good and selective concentration and a long retention in the tumor, as is generally the case in neuroblastoma, are the basis for successful 131I-MIBG treatment. At The Netherlands Cancer Institute a phase II study was carried out in 53 patients with progressive recurrent disease after conventional therapy had failed. Despite the unfavorable basis for treatment, 131I-MIBG therapy induced 7 complete remissions, 23 partial remissions and arrest of disease (no change) in 10. Nine patients had progressive disease and one patient was lost to follow-up. The palliative effect of the treatment under these conditions was impressive. The duration of remissions varied from 2 to 38 months. The best results were obtained in patients with voluminous soft tissue disease. In general the treatment was well tolerated by children and the toxicity was mild, provided the bone marrow was not invaded by the disease. It is concluded that 131I-MIBG therapy has a definitive place in the treatment of neuroblastoma after conventional treatment has failed. As the invasiveness and toxicity of this therapy compare favorably with that of chemotherapy, immunotherapy and external beam radiotherapy, 131I-MIBG therapy is the best palliative treatment for patients with advanced recurrent neuroblastoma.