Peptide-receptor radionuclide therapy (PRRT) with radiolabeled somatostatin analogs is a promising option for the treatment of somatostatin-receptor-positive endocrine tumors. Treatment with somatostatin analogs labeled with (111)In, (90)Y or (177)Lu can result in symptomatic improvement, although tumor remission is seldom achieved with (111)In-labeled analogs. In this Review, the findings of several studies on the use of PRRT for endocrine tumors are evaluated. Large variation in the antitumor effects of (90)Y-octreotide was reported between studies: an objective response (> or =50% tumor regression) was achieved in 9-33% of patients. After treatment with (177)Lu-octreotate, an objective response was achieved in 29% of patients and a minor response (25-50% tumor regression) was achieved in 16% of patients; stable disease was present in 35% of patients. Treatment with (177)Lu-octreotate resulted in a survival benefit of several years and markedly improved quality of life. Serious, delayed adverse effects were rare after PRRT. Although randomized, clinical trials have not yet been performed, data on the use of PRRT compare favorably with those from other treatment approaches, such as chemotherapy. If these results can be replicated in large, controlled trials, PRRT might become the preferred option in patients with metastatic or inoperable gastroenteropancreatic neuroendocrine tumors.