BACKGROUND: Langerhans cell histiocytosis (LCH) is a rare disease that involves a clonal proliferation of Langerhans cells. LCH has a predilection for hypothalamo-pituitary axis (HPA) dysfunction, and this leads to diabetes insipidus (DI) and/or anterior pituitary dysfunction. Here, we describe the endocrine dysfunction and clinical characteristics of adult patients with LCH and we analyzed the differences between an adult-onset type and a childhood-onset type. METHODS: The data was obtained from a retrospective chart review of the patients with LCH that involved the HPA and who attended Seoul National University Hospital. The patients were classified into the adult-onset type (age at the time of diagnosis > or = 16) and the childhood-onset type (age at the time of diagnosis < or = 15). RESULTS: Ten patients (9 males and 1 female) were diagnosed with LCH involving the HPA. Five patients were classified as an adultonset type and the other five patients were classified as a childhood-onset type. The median follow-up duration was 6 (3-12) years for the adult-onset type and 16 (15-22) years for the childhood-onset type. All the patients presented with DI as the initial manifestation of HPA involvement. Four adult-onset patients and three childhood-onset patients had a multi-system disease. Panhypopituitarism developed in three adult-onset patients and in one childhood-onset patient. The pituitary lesion of the three adult-onset patients had spread to the brain during the follow-up duration. In contrast, the pituitary lesion of the other two adult-onset patients without panhypopituitarism and all the childhood-onset patients had not changed. CONCLUSION: DI was the initial presentation symptom of HPA involvement. Anterior pituitary hormone deficiency followed in some patients. Compared with the childhood-onset patients, the adult-onset patients were more likely to have panhypopituitarism and a poor prognosis.