We herein report a case of solitary cutaneous reticulum cell tumor not associated with any other organ involvement. The enzyme-immunohistochemical and electron-microscopic features of the cellular infiltrate are the same as those of interdigitating reticulum cells (IDRC), which can give rise to neoplasms in lymphoid organs; they are also similar to those of Langerhans cells and “indeterminate” cells, which are usually thought to give rise only to systemic disorders. The authors support the hypothesis that such neoplasms may represent the cutaneous counterpart of IDRC neoplasms of lymphoid organs.