A 76-year-old woman with a perianal erythema was found to have extramammary Paget's disease by histopathologic examination. The Paget's cells were immunohistochemically positive for CK20 and villin, but negative for CK7 and GCDFP15. These results strongly suggested that her lesion was secondary from ano-rectal adenocarcinoma. We decided to perform a laparoscopic abdomino-perineal resection in spite of the negative results of pre-operative proctoscopy and lower gastro interstitial endoscopy. Histologically, Paget's cells were seen in the epithelium throughout the perianal skin to the dentate line. In addition, there were some discrete foci of glandular structures composed of signet ring-like atypical cells in the submucosa of the dentate line. She was finally diagnosed with occult anal canal carcinoma secondary to perianal Paget's disease.