We reported relatively rare cases of carcinoid tumor of gastro-intestinal tract. Case 1 is a 51 year-old male with dysphagia and epigastric pain. X-ray examination of the stomach revealed cardiac tumor of Borrmann II type on the lesser curvature and biopsy specimen from gastric endoscopy was diagnosed as undifferentiated carcinoma. He was operated on. Histologically, the lesion was gastric carcinoid tumor with many argyrophil positive granules in their cytoplasm by Grimelius stain. After operation, he had left hemiplegia and episodes of asthma but urinary excretion of 5-HIAA was within normal limits. Death occurred 44 days after operation. Autopsy showed metastatic carcinoid tumor in the liver, right cerebral hemisphere, pancreas and thyroid gland. Case 2 is a 74 year-old male with abdominal fullness. On examination, emaciation of moderate degree was present. Abdomen was protruded and large volume of ascites was demonstrated. A semifixed fist-sized mass was palpable in the upper abdomen. Roentgenograms and endoscopy of the stomach were performed but clear evidence of gastric malignancy was not obtained. His chief clinical trouble was intractable ascites which did not respond to various drug treatments. Ascites was transudate in nature and Papanicolaou's cytology was always class 1. Death occuurred 25 days after hospitalization. Autopsy disclosed two large tumors in the stomach; one, measuring 6.0×6.5cm, was Borrmann II type tumor localized on the pyloric antrum and the other one, measuring 6.0×4.7×4.0cm, was localized in the submucosa of the fundic segment. Histologically two lesions were fundamentally of the same nature, showing many argyrophil granules in their tumor cells and diagnosed as carcinoid tumor of the stomach. Metastasis was demonstrated in the liver and regional lymph nodes. Moreover, direct invasion of the tumor into the portal vein associated with many tumor thrombi in portal tributaries in the liver was a conspicuous finding of this case. Case 3 was a 81 year-old male with melena. X-ray and endoscopic examination revealed a rectal tumor of Borrmann II type. A diagnosis of adenocarcinoma was confirmed from the biopsy specimen. The resected specimen showed a tumor of Borrmann II type, measuring 2.0×2.5cm and a small polypoid tumor covered with normal mucosa near the large Borrmann II type tumor. Histologically, the large tumor was adenocarcinoma of Dukes A and small one was carcinoid tumor with many argyrophil granules in their cytoplasm. Metastasis of both tumors was not demonstrated. The patient made an uneventful convalescence and was alive ten months after operation. According to statistics based on "Annual of the Pathological Autopsy Cases in Japan", cases of carcinoid in 3 years (1974-1976) amounted to 75(0.11% of the whole autopsy cases). Of these carcinoid cases, associated other malignancy was demonstrated in 22 cases (29%). There appears to be an increased incidence of other malignant neoplasms associated with carcinoid tumors in comparison with the incidence of double malignant tumors excluded carcinoid tumor.