Patients with metastatic carcinoid tumors and the malignant carcinoid syndrome have benefited immensely from diagnostic and therapeutic advances during the past decade. Magnetic resonance imaging and whole body scintigraphy with radiolabelled analogues of somatostatin have improved our ability to diagnose, detect, stage and follow response to therapy. Surgical, medical, and radiation therapy may all contribute to the management of these patients. This disease is variable in its presenting symptoms and the biologic behavior of the tumor. The spectrum of clinical manifestations varies depending upon the type and quantity of polypeptide hormones or biogenic amines being produced. Although the tumors are usually indolent in their growth, the more dedifferentiated or anaplastic tumors can be quite aggressive. Thanks to new treatments that are very effective in the subgroup of anaplastic neuroendocrine carcinomas it is vital to recognize this subset. As research scientists and clinicians we must be aware of the natural history of the disease in order to optimize each patient's treatment. This highly selective review focuses on studies performed in collaboration with Dr. Charles Moertel along with other colleagues at the Mayo Clinic, have done in the past few years.