We report a case of a bright, alert patient with central neurogenic hyperventilation (CNH) associated with cerebral malignant lymphoma. CNH is a syndrome comprising normal or elevated arterial oxygen tension, decreased arterial carbon dioxide tension, and respiratory alkalosis in the absence of cardiac or pulmonary disease that stimulates a compensatory hyperpnea. A-72-year-old man with recurrent central nervous system lymphoma presented with hyperpnea. showing a respiratory rate over 30 per minute. He was fully awake and conscious. Routine laboratory studies and chest X-ray were normal, but arterial blood gas examination on room air showed respiratory alkalosis, regardless of wakefulness or sleep. Pulmonary infarction was denied by pulmonary flow scintigram. Rebreathing from a paper bag, intravenous administration of diazepam, and oxygen inhalation failed to alter the respiratory pattern. Brain MRI demonstrated two mildly enhanced lesions within the left side of the medulla oblongata and right side of the pons. CNH is rare in patients with normal consciousness. It seems to be caused by brainstem injury that includes the respiratory center.