LCH is a rare proliferative histiocytic disorder, and it can infiltrate virtually any site in the body. Diabetes incipidus (DI) is the most common abnormality when there is involvement of the hypothalamic-pituitary axis (HPA). We have evaluated the anterior pituitary function and their responses to treatment in 9 patients (5M/4F; range 1960 years) with proven LCH and DI. Endocrine evaluations consisted of clinical history, basal (GH, IGF-1, fT4, TSH, PRL, cortisol, LH, FSH, E2, and testosteron levels) and dynamic pituitary function tests, plasma and urine osmolalities/water deprivation test at the time of diagnosis of DI and thereafter. The mean age at onset of DI was 28 years (1560). Radiological evaluation included MRI of the HPA region. Three patients with infundibular and one patient with thalamic involvement were treated with local radiotherapy (RT). Chemotherapy and local (bone) RT combination had been given to 3 patients with bone lesions, and another 2 had been treated with chemotherapy alone. Median follow-up period was 74 month (2300). On admission, single-organ involvement in one of the patients, and multisystem involvement in the remaining 6 patients were found. In addition to DI, diagnosis of secondary hypogonadism was established in only one patient who had no signs of puberty but normal PRL level. Another one had also secondary hypothyroidism, hypocortisolism, and hypogonadism with thalamic involvement. The other 2 patients did not suffer from any additional abnormalities concomittant with the initial DI. Hyperprolactinemia was found in 3 patients (43%). MRIs showed infundibular enlargement (89%), thalamic mass (11%), and the absence of the bright spot (100%) on the T1-weighted sequences. One patient had an additional mass in the pons with partially empty sella. Two patients who had received local RT to the pituitary stalk achieved complete radiological responses, and gonadotropin deficiency also recovered in one of them. One patient with pons and another with thalamic involvement died after therapy. Until now, GH deficiency developed in 5 patients and partial gonadotrophin deficiency in another patient. Seven patients are currently under regular follow-up with stable disease, but DI persisted in all patients. As a result, DI in LCH was the earliest hormonal deficiency. Localized RT can be successfully applied as a single treatment for infundibuler involvement or in combination with chemotherapy leads to high remission and local control rates.