Extranodal natural killer/T-cell lymphoma (ENKTL) is a distinct subtype of non-Hodgkin's lymphoma and is rare in the colon. Synchronous adenocarcinoma and ENKTL of the colon has not been reported in the literature. In the present study, we report a 63-year-old male who suffered from intermittent bloody stools for 2 mo. He did not have fever, body weight loss or night sweat. Endoscopic and imaging studies revealed a 4.5-cm ulcerative mass in the ascending colon and a 3.0-cm polypoid, easy bleeding mass in the sigmoid colon, respectively. Thought to have double carcinoma of the colon, he received simultaneous right hemicolectomy and sigmoidectomy. The pathological diagnosis was a synchronous ENKTL (ascending colon) and adenocarcinoma (sigmoid colon). The literature on synchronous adenocarcinoma and malignant lymphoma of the colon was also reviewed.