Clinical data about 104 patients with gastrointestinal carcinoids emphasized the heterogeneous nature of these tumours in different organs. The sites of the primary tumours were the stomach in 12 (11%), the duodenum in 3 (3%), the small bowel in 48 (45%), the appendix in 28 (26%), the colon in 6 (6%), and the rectum in 6 cases (6%). Gastric carcinoids were multiple in 4 (33%) and small-bowel carcinoids in 11 cases (23%). None of the gastric, duodenal, or rectal carcinoids had generated metastases, as contrasted to 34 (72%) small-bowel carcinoids. Twelve patients had symptoms of the carcinoid syndrome caused by hepatic metastases from ileal (11) or appendiceal (1) primary tumours. At least two patients with duodenal carcinoids had Zollinger-Ellison syndrome produced by the tumours. The cumulative 5-year survival rate was 91-100% for gastric, appendiceal, and rectal carcinoids, 77% for small-bowel carcinoids, and 33% for colonic carcinoids. Resectable mesenteric lymph node metastases did not affect the 5-year survival of patients with small-bowel carcinoids as compared with the tumours confined to the bowel wall. Poor prognosis was associated with hepatic metastases at the time of diagnosis. Small-bowel carcinoids remain a challenge in clinical work because of their distinct metastatic propensity and problematic diagnosis.