Proliferations of Langerhans cells can be histologically divided into cytologically benign Langerhans cell proliferations, which include the clinical syndromes of Langerhans cell histiocytosis, and cytologically malignant Langerhans cell sarcoma. We report a Langerhans cell sarcoma in a 33-year-old male that arose on the posterior thigh with subsequent regional lymph node involvement. Conventional microscopic, immunohistochemical, and ultrastructural analysis confirmed Langerhans cell differentiation. Aberrant CD31 expression, similar to that described previously in Langerhans cell histiocytosis, was prominent in this tumor, possibly enhancing its migratory capabilities.