Gastrocolic fistula (GCF) secondary to colon carcinoma is a rare entity. Establishing the diagnosis of GCF is difficult because it has nonspecific symptoms on admission. The characteristic triad of clinical manifestations includes diarrhoea, faeculent vomiting, and weight loss. Surgical treatment of GCF involves en-bloc resection of the involved regions and appropriate reconstruction procedures for malignant cases. The authors hereby report a 54-year-old man with a 2 months history of weight loss, watery diarrhoea, fecal halitosis and melena. Laboratory tests showed severe anaemia and hypoalbuminaemia. The GCF was detected successfully by CT scan, barium meal and colonoscopy, but could not be seen on gastroscopy. A radical en-bloc resection was performed and histological examinations revealed a low-differentiated adenocarcinoma of the colon.