Three cases of colon cancer accompanied by unusual abscess formation are reported. Case I : A 77-year-old man was diagnosed with a paracolic abscess formation behind the cecum and a swollen appendix by computed tomography (CT) scan. Case II : An 85-year-old woman was diagnosed with an abscess formation of the right iliopsoas muscle, a swollen appendix, and a thickened right colon wall by CT scan. After antibiotic therapy failed, both patients underwent ileocecal resection urgently under suspicion of appendicitis, but cecal cancer around the entrance to the appendix caused secondary appendicitis in both cases. Case III : A 50-year-old woman was diagnosed with sigmoid colon cancer with an abscess formation in the pelvic cavity concomitant with ovarian tumor. A Hartmann procedure was performed, and a pathological examination revealed that a subserosal abscess behind the sigmoid colon cancer perforated the rectum with abscess formation. All cases were definitively diagnosed intraoperatively. The cancer recurred in cases I and III. We emphasize that precise surgical evaluation has an important role in the diagnosis of these complicated diseases. In addition, surgery affords the patient the best chance of recovery, and in these advanced cases radical treatment is recommended as early as possible