Background: I-131 Metaiodobenzylguanidine (MIBG) is a radiopharmaceutical which is proved effective in treatment of tumors with neuroendocrine origin, especially the neuroectodermal (sympathoadrenal) type, including pheochromocytoma, paraganglioma and neuroblastoma. It is also of some value in other neuroendocrine tumors (mainly carcinoid and medullary carcinoma of thyroid). Methods: The method employed in this research was a systematic bibliographic review, in which only valid studies or the clinically detailed enough open-labeled studies using validated scales were used. Results: I-131 MIBG is the best nonsurgical method for treatment of pheochromocytoma. It not only increases survival, but also significantly improves patients’ symptoms (75-90%). Although the efficacy of this method for refractory or relapsing neuroblastoma has been 30%, adding other treatment modalities increases the impact of this treatment. For other neuroendocrine tumors including carcinoid tumor and medullary carcinoma of thyroid, MIBG therapy has been effective in reducing patients’ symptoms. The most important complication of this method is myelosuppression which needs follow-up and if necessary relevant treatment. Conclusion: I-131 MIBG has an important role in treatment of chromafin tumors. For pheochromocytoma and neuroblastoma it is the best nonsurgical treatment. It is effective in neuroblastoma especially if it is used in conjunction with other treatment modalities. I-131 MIBG can also diminish symptoms of carcinoid tumor and medullary thyroid carcinoma efficiently.