Malignant carcinoid tumors are remarkably varied in their biologic behavior. The disease may be indolent for years with minimal or no symptoms. On the other hand, an acute carcinoid crisis with severe diarrhea, dehydration, and hypotension may develop in the patient. Patients with flushing and/or diarrhea, not responsive to standard symptomatic measures, may benefit from chemotherapy or hormonal therapy. Chemotherapy with single agents or combination chemotherapy may be associated with response rates ranging from 20 to 40 percent. Hepatic de-arterialization by ligation or occlusion is an effective means of inducing rapid tumor shrinkage for patients who have carcinoid tumors and hepatic dominant metastases. The addition of chemotherapy after induction of a partial remission with hepatic de-arterialization may prolong the duration of response, but this remains to be proven in prospective clinical trials. Hormonal therapy with the antiestrogen tamoxifen has been unsuccessful, but treatment of the carcinoid syndrome with a long-acting analogue of somatostatin has been strikingly effective.