An unusual case of cutaneous and hypothalamic histiocytosis X (HX) is reported. The hypothalamic involvement occurred as a tumor that mimicked a chiasm glioma on computed tomography angioscanning. Magnetic resonance imaging after gadolinium injection localized the tumor within the third ventricle floor. The HX origin of the tumor was confirmed by histological examination of hypothalamic biopsies obtained by transventricular endoscopy. The results of endocrine evaluation were consistent with anterior panhypopituitarism resulting from a multiple releasing-hormone secretory defect, but there was no diabetes insipidus. This unusual endocrine aspect has not been previously described in the field of hypothalamic HX. Lastly, the tumor was insensitive to low dose megavoltage radiation therapy. This unusual case stresses the superiority of magnetic resonance imaging over computed tomography scanning in the assessment of suprasellar tumors and emphasizes the usefulness of transventricular endoscopy in these cases.