Background: A previously unrecognized erythema was noted in 6 patients with extramammary Paget’s disease (EMPD) of the genitalia with metastases. It was distinct from essential erythema of EMPD and has not been reported before. Objective: Our purpose was to describe the clinical and histopathologic features of the erythema and clarify its pathogenesis and prognostic importance. Methods: A review of the clinical records and histologic materials of 6 cases was made focusing on the clinical features of this unique erythema as well as the course and prognosis of the patients. Results: The erythema first appeared in the inguinal region and extended centrifugally to an area normally covered by underpants. Histopathologic examination showed lymphatic infiltration by cancer cells of the skin. All of the patients with this “underpants-pattern erythema” died of the disease, and the mean survival period after its appearance was 13 months. Conclusion: Underpants-distribution erythema may be a sign of advanced stage EMPD. (J Am Acad Dermatol 1999;40:949-56.)