Nevus depigmentosus is a stable and well-circumscribed congenital hypomelanosis that may be in an isolated, dermatomal or systemic form. An 18-yr-old Korean man with segmental nevus depigmentosus developed multiple pigmented nevi which were present only within the confines of the leukoderma. Histologic and electron microscopic studies rendered a diagnosis of nevus depigmentosus with dysplastic nevus to the patient. The genetic alteration of melanocytes in the hypopigmented lesion is assumed to have resulted in the development of multiple pigmented nevi.