Slow-growing brain tumors can produce disturbances of food intake and endocrine dysfunction. We report a case of slow-growing midline brain tumor in a patient with clinical presentation of anorexia nervosa (AN). A 19-year-old man was referred from a general practitioner to a psychiatric clinic due to illness behavior and psychopathological characteristics of AN. His body weight had decreased from 52 kg to 40 kg within 6 months. Laboratory tests showed hypernatremia (160 mmol/L), adrenal insufficiency (adrenocorticotrophic hormone, 11.4 pg/mL; 8 am cortisol, 1.4 microg/dL; 4 pm cortisol, 11.4 microg/dL) and hypogonadotropic hypogonadism (testosterone < 0.5 ng/mL, follicle-stimulating hormone < 0.1 mIU/mL, luteinizing hormone < 0.7 mIU/mL). Brain magnetic resonance imaging showed an extensive mass lesion at suprasellar, hypothalamic region, third ventricle, pineal region, lateral ventricle, and corpus callosum. Owing to central herniation during physical assessment, he died of unknown intracranial pathology. This case suggests that an intracranial tumor near the hypothalamus should be included in the differential diagnosis of AN. Any male adolescent with the clinical impression of AN should receive periodic re-evaluation, including neurological, endocrinological and, if necessary, neuroimaging study.