No statistical evaluation of patients with carcinoid syndrome in a reliable number of cases has been available in the past 35 years. To update our knowledge about the syndrome, we have evaluated from various clinicopathologic viewpoints a large series of patients with the syndrome reported up to date. The data of 748 patients with the syndrome were collected from 8876 carcinoid patients reported in the literature and analyzed by the Gut-Pancreatic Endocrinoma Analyzing System (the Niigata Registry). The results are summarized as follows. 1) The patients with the syndrome had a tendency to be older than those without it. 2) The incidence of the syndrome was 8.4% of 8876 carcinoid patients. 3) Serotonin activities were extremely high in patients with the syndrome as compared to those without it (91.7% versus 26.6%). 4) The rate of metastases was higher in patients with the syndrome than in those without it (84.8% versus 29.2%), and higher in the liver than in lymph nodes among patients with the syndrome (73.4% versus 37.4%). 5) Flushing and carcinoid heart as most specific clinical manifestations of the syndrome were recorded at 78.3% and 17.4%, respectively. 6) The 5-year survival rate after resection of primary lesions was 76.0% of 304 patients with the syndrome, lower in patients with digestive carcinoids than in those with extradigestive lesions (67.2% versus 88.7%). It is expected that the results obtained in the present evaluation on patients with carcinoid syndrome will provide investigators active in this specialized field with useful and extensive information for their future activities.