Abstract: A 57-year-old man was admitted to the hospital for a 7-year progressively spreading plaques involving the entire body surface, and multiple irregularly sized red nodules and infiltrated patches on the face, trunk and limbs. Histopathological examination showed pleomorphic tumor cells diffusely dispersed throughout the dermis, giving an appearance of low proliferation. Some cells with cytoplasmic processes appeared multiangular in shape. Immunohistochemically, tumor cells were negative for CD1a or S-100, but positive for CD45, FXIIIa, CD14, MHC-Ⅱ, CD68 and lysozyme with extracellular interstitial expression. Ultrastructurally, the cells exhibited cytoplasmic processes and irregularly sized nuclei; no Birbeck granules were observed. Vesicules of low electron-density were seen diffusely in cytoplasm and extracellular matrix. The case is herein diagnosed as cutaneous non-Langerhans cell histiocytosis, which presents with a chronically invasive clinical course. These cells may develop from immature dermal dendritic cells.

Key words: Skin, dendritic cells, histiocytosis, FXIIIa