Paget's disease most commonly affects the breast. Extramammary involvement is rare, and the most commonly affected sites are the vulva, anus, perianal region, and axilla. The disease may progress to invasive adenocarcinoma or synchronous cancers. Due to the lack of distinctive features and nonspecific presenting symptoms, Paget's disease may be misdiagnosed as other conditions, thus delaying the correct diagnosis. We report a case of extramammary Paget's disease in the perianal region that initially presented as an irregular, circumferential, scaling lesion with eczematous eruptions. Immunology and immunohistochemistry confirmed the diagnosis. Although surgery is the standard treatment, the patient opted for pelvic radiotherapy associated with radiosensitizing chemotherapy.