The carcinoid syndrome, associated with carcinoid tumors of the midgut, consists of symptoms such as diarrhea, flushing, wheezing and cardiovascular symptoms. This review focuses on these symptoms and discusses therapeutic options. The symptoms are caused by the secretion of biogenic amines, polypeptides and other factors of which serotonin is the most prominent. However, diarrhea is also due to factors such as malabsorption. Besides antitumor therapy, more specific interventions such as serotonin receptor blockers can be useful. The carcinoid heart disease involves the tricuspid and pulmonary valve. In the pathogenesis, serotonin plays a central role. The therapeutic approach is mostly symptomatic. Other cardiovascular complications include bowel ischemia and hypertension. Pellagra and psychiatric symptoms are due to a depletion of tryptophan, which is consumed by the carcinoid tumor for serotonin synthesis. Finally, follow-up and clinical practice of patients with carcinoid tumors are discussed.