A 58-year-old man had widespread multiple erythemas that had been untreated for 20 years. The cutaneous lesions increased in size for a year. Histopathological examination revealed increased number of large, dysplastic, histiocytic cells in the dermis; most of these cells tested positive for Langelin, CD1a and S-100 staining. The patient was diagnosed with Langerhans cell histiocytosis (LCH) and treated with narrow-band ultraviolet B (NB-UVB) radiation. The erythema improved after treatment, but the tumor remained. Therefore, the tumor was surgically excised. NB-UVB therapy might be effective for the treatment of superficial lesions, but not tumoral lesions of LCH.