The intent of this study was to evaluate the safety and efficacy of high-activity 111In-pentetreotide in patients with neuroendocrine tumors. Thirty-two patients with pentetreotide-avid neuroendocrine tumors received therapy from August 2005 to November 2006. Fourteen (14) patients received 1 treatment and 18 patients received 2 treatments. Patients were followed an average of 12.73 months (range 1.2-24.5). Seventeen (17) patients (53%) had grade I or II hematologic toxicities, and 1 patient had grade III thrombocytopenia. One patient had grade II liver toxicity, which appeared 4 weeks after therapy and resolved on week 5. No patient had renal toxicity. Of the patients who completed 2 treatment cycles, 2 of 18 patients had partial disease regression, and 16 of 18 patients with previously progressive disseminated neuroendocrine disease achieved stable disease by imaging criteria. A decrease in serum tumor markers was observed in 14 of 18 patients given 2 therapies. A clinical response was achieved in 84% of the patients. Upon interim analysis, median survival was approximately 13 months (range 1.2-24.5). These results show that high-activity 111In-pentetreotide therapy is effective in patients with progressive disseminated neuroendocrine tumors.