In 2006, while admitted in our hospital for surgical treatment of recurrent diverticulitis, a 54-year-old man was found to have an adenocarcinoma arising within a colonic diverticulum. Computed tomography, during this episode of diverticulitis, showed a thickened wall of the sigmoid and inflammatory induration of the pericolonic fat. Colonoscopy could be performed up to no more then 25 cm from the anus due to mucosal edema. A sigmoid resection was performed. Histopathological examination of the resected specimen showed an inflamed diverticulum with a submucosal adenocarcinoma of the intestinal type within its wall. The surrounding flat colonic mucosa was not involved by the cancerous process. Due to lymph node involvement the patient received adjuvant chemotherapy and remained disease free during follow up.