An exophytic adenocarcinoma of the colon is very rare with only a few reports to date. To the best of our knowledge, the CT appearance of colon cancer, which simulated the classic appearance of a GIST has only been reported once in the world's literature. We recently evaluated a patient with a large lobulated mass involving the stomach, pancreas and colon. The CT appearance of the case was consistent with the diagnosis of an exophytic gastric GIST. However, at surgery, the patient was found to have a large ulcerated carcinoma of the colon near the splenic flexure that had invaded the stomach and pancreas. We report a case of an exophytic adenocarcinoma of the colon that resembled the classic appearance of a gastrointestinal stromal tumor of the stomach.