Diabetes insipidus (DI) in Langerhans cell histiocytosis (LCH) is a common complication of unclear etiology. The incidence varies among different publications from 15% to 50%. In the prospective DAL-HX 83 study, 19 out of 199 patients (9.5%) registered with newly diagnosed LCH were diagnosed to have DI. All patients were stratified according to uniform criteria. One hundred and six patients with disseminated disease were treated with standardized polychemotherapy promptly after diagnosis. At the time of diagnosis of LCH, DI was already established in 8 out of 199 patients (4%). After diagnosis, DI occurred in only one out of the remaining 91 patients with localized disease (1%) and in 10 out of 100 remaining patients with disseminated disease (10%). In 8 patients, the onset of DI was associated with other signs of active LCH. The cumulative risk to develop DI after a median observation time of 5 years 3 months was 11%. Retrospective analysis of clinical features revealed multisystem involvement, skull and orbital lesions, and in particular intracranial extension from osseous lesions to constitute risk factors for DI. Magnetic resonance imaging studies (MRI) were available in 12 patients and showed abnormalities of the pituitary region in 10 children. In none of the patients with established DI was it reversed or ameliorated by any treatment. However, the rapid institution of systemic chemotherapy for disseminated disease seems to prevent the occurrence of DI and may be responsible for the low frequency of DI in the DAL-HX83 study.