Primary objective - Provide access to therapy with 131i-metaiodobenzylguanidine (131i-MiBG) for patients with relapsed/ refractory neuroblastoma or metastatic pheochromocytoma Secondary objectives - assess disease response to 131i-MiBG therapy for patients with relapsed/refractory neuroblastoma or metastatic pheochromocytoma - Gain more information about the toxicities of 131i-MiBG therapy - assess improvement of symptoms, including pain and fatigue, for patients with relapsed/refractory neuroblastoma or metastatic pheochromocytoma who are receiving 131i-MiBG therapy. 131i-MiBG has undergone multiple trials for the treatment of malignant pheochromocytoma and neuroblastoma. The results from these trials show that MiBG is active against refractory neuroblastoma with an objective response rate of [Greater Than]40% and disease stabilization in another 30-40% of patients. The current study will provide a mechanism to provide this highly effective agent to patients not eligible for other MiBG or other investigational agent therapies. it also will provide a mechanism to collect and describe long-term safety and efficacy data.