Evaluation of the response of histiocytosis χ to various forms of treatment is difficult, because presentation patterns are protean and the disease can be self-limited. A retrospective evaluation was made of the healing of 42 histiocytosis χ bone lesions, in 21 patients treated in variety of ways, using serial radiographs and a semiquantitative scoring system. Treatments included various combinations of surgery (simple biopsy or curettage), radiotherapy (200 to 1,200 centi-Gray [cGy]), chemotherapy (according to various protocols), and local steroid injection. Median times to a given degree of healing were similar across treatment groups and in untreated lesions. It was concluded that mode of treatment does not exert a strong influence on the rate of healing of histiocytosis χ bone lesions. Some healing should be apparent 4 months after diagnosis, but complete healing may take many months. Treatment of histiocytosis χ bone lesions is indicated only if intense pain or risk of fracture or deformity are present.