AB Premalignant lesions of the anal margin include Bowen's disease (intraepithelial squamous cell carcinoma) and Paget's disease (intraepithelial adenocarcinoma). Our experience includes 11 patients with perianal Paget's disease and 37 patients with perianal Bowen's disease treated from 1957 to 1986. The patients with perianal Paget's disease were older, had a higher incidence of invasive cancer, and had a worse prognosis than those with perianal Bowen's disease. The characteristic appearance of these lesions and their failure to respond to conventional therapy should lead the clinician to obtain a biopsy, which readily establishes the diagnosis. Our experience confirms that adequate evaluation followed by wide local excision is the appropriate therapy. Close follow-up is recommended to identify recurrence of the perianal disease or development of other malignancies.