A case of locally extensive perianal Paget's disease is presented. Initial wide local excision, guided by frozen sections, was inadequate. Multiple punch biopsies subsequently revealed extensive circumferential involvement of the anoderm by Paget's disease, making wide local excision difficult. Therefore, the patient was treated with combined chemoradiotherapy (5000 cGy, 5-fluorouracil, and mitomycin C). Fourteen months after treatment, the patient had a complete response.