The brains of eight patient with Langerhans Cell Histiocytosis (LCH) were studied with magnetic Resonance Imaging (MRI). One scan was normal and a spectrum of abnormalities was seen in the others. Five patients had absence of the posterior pituitary bright spot, and four with evidence of pituitary dysfunction had a lesion in the region of the hypothalamus. An orbital extraconal mass was noted in one child with exopthalmus. This decreased in a follow-up study after Vinblastine therapy. The cerebellum was abnormal in two patients; the area of the dentate nuclei exhibited abnormal signal in one asymptomatic child and the MRI of another boy with a ten year history of progressive cerebellar dysfunction showed cerebral and cerebellar atrophy. Three of the five patients with deficiency of antidiuretic hormone (ADH) were studied both before and after the administration of intravenous Gadolinium-DTPA. In all three, after administration of the contrast agent, there was enhancement of involved areas.