Thirty-two patients with histiocytosis X were evaluated and treated at Children's Memorial Hospital, Chicago, during the years 1978 to 1984. Twelve patients (38%) had solitary or multifocal bone lesions, three (9%) had bone lesions and diabetes insipidus, and seventeen (53%) had cutaneous and/or multisystem involvement. Age at diagnosis ranged from 2 days to 15 years. Fifteen patients were 2 years of age or younger at the time of diagnosis. Sixteen patients (50%) had skin infiltrates, of whom seven (43%) had cutaneous lesions documented at birth. Cutaneous lesions included vesicopustules, erythematous papules, nodules, eczematous dermatitis, granulomatous ulcerative lesions, petechiae, and hemorrhagic lesions. Xanthomas and nail dystrophy were not observed. The therapeutic regimen chosen was based on extent of involvement and location of infiltrates. Only two of the thirty-two patients died; both had multisystem disease.