In February 2007, a 76-year-old man underwent endoscopic mucosal resection (EMR) for sigmoid colon cancer. Histological examination of the EMR specimen revealed adenocarcinoma in adenoma that was confined to the mucosal layer, and pathological complete resection was achieved. Since then, the patient has been followed up every year with endoscopic examination of the colon, with normal results except for hemorrhoids. In June 2011, a positive result for occult blood was obtained on examination of a stool sample. In July 2011, enhanced computed tomography of the chest and abdomen was performed, and the left supraclavicular, paraaortic, and left common iliac artery lymph nodes were found to be enlarged. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) identified accumulation of 18F-FDG in the enlarged lymph nodes. Histopathological examination of a biopsy specimen from the left supraclavicular lymph node revealed tuberculous changes; therefore, the patient was administered anti-tuberculosis therapy. The culture isolate of the above lymphatic tissue specimen was identified as Mycobacterium tuberculosis by immunochromatographic assay with MPB64 protein (Capilia TB). Laparoscopic examination of abdominal lymph nodes was not performed because the patient's consent could not be obtained. After the anti-tuberculosis therapy, the size of the abdominal lymph nodes was reduced, and subsequently, 18F-FDG accumulation decreased. It is considered that mucosal colon cancer did not spread to the lymph nodes after it was removed completely. For the definitive diagnosis of abdominal lymph node swelling, it would have been necessary to perform laparoscopic examination, which was impossible in this case. When it is difficult to perform invasive examinations, such as laparoscopy in case of swelling of the abdominal lymph node, 18F-FDG PET/CT can be useful for monitoring the therapeutic response of abdominal tuberculosis.