A male child first presented with chronic perianal skin disease at 33 months of age and later developed gingival disease and loose teeth associated with alveolar bone erosion. Biopsy of gingival and perianal lesions showed histiocytic proliferation. Following therapy with vinblastine, prednisone, methotrexate, and cyclophosphamide, the lesions healed but disease recurred in the mastoid and was successfully treated with vinblastine alone. Although the perianal area is an unusual site of skin involvement in systemic histiocytosis, this disorder should be considered in any child with chronic unexplained perianal disease, and biopsy of these lesions should be obtained.