Forty children who had Langerhans-cell histiocytosis were followed for an average of six years (range, excluding patients who died of the disease, two to fifteen years). The patients were divided into two diagnostic groups: those who had localized disease (involving one bone or more only) and those who had multifocal disease (an osseous lesion and a soft-tissue mass, a skin rash, diabetes insipidus, or generalized disease). Methods of treatment included curettage, bone-grafting, chemotherapy, local or systemic corticosteroids, and radiotherapy. Nineteen of the thirty patients who had localized disease had a complete response to the therapy, four had a partial response, and seven had no response. Twenty-one of these thirty patients had not had a recurrence by the time of the latest follow-up examination; nine had a local recurrence within four years after the initial therapy but had no additional recurrences after treatment of the local recurrence. No recurrence occurred more than four years after the time that the initial diagnosis had been made. Five of the ten patients who had multifocal disease had a complete response to the therapy, two had a partial response, and three had no response. Six patients had a recurrence; four did not. Two patients died of the disease. As a result of this study, we recommend the avoidance of intensive measures of treatment, if possible, and we advise long-term follow-up of these patients.