Concurrent occurrence of an adenocarcinoma and carcinoid tumor in the stomach has been observed infrequently; moreover, a gastric collision tumor of both tumor types has rarely been seen. We describe a case of a gastric collision tumor following the differential diagnosis from observing the morphological patterns more closely using CT gastrography. The patient presented with a gastric collision tumor that consisted of an adenocarcinoma and carcinoid tumor in the antrum of the stomach.