For the treatment of extramammary Paget's disease (EMPD), wide excision has been recommended because of unpredictable spread of tumor cells. EMPD lesions are often well circumscribed. Should all the lesions of EMPD be resected with a 3 cm margin? Forty-six patients with EMPD were surgically treated with a 1 cm margin. Width of tumor cell free area from the last lesional cells at the borders to the resected edge was measured with micro-oculometer. The microscopic gap between the histopathological tumor border and the clinical border scored by scalpel tract was also measured. The tumor cell free area measured 10.2 +/- 2.48 mm. The microscopic gap between the histopathological and clinical borders measured 0.334 +/- 1.183 mm. Thus, the clinically determined border of well-defined lesions of EMPD corresponded well to the histopathologic border. No local recurrence was observed in 24 to 115 months of follow-up. Well-demarcated lesions of EMPD can be adequately managed with 1 cm margin resection.