Slowly growing intracranial tumors, especially located in the supratentorial compartment, permit major volume-spacial compensation. Patient with large supratentorial tumor may not even present any specific symptoms or signs related to the elevated intracranial pressure. We experienced a patient who showed delayed emergence from general anesthesia for total knee replacement without any pharmacologic or metabolic causes. Computerized tomogram scan and magnetic resonance image revealed an unnoticed large supratentorial tumor considered as a cause of delayed emergence. After removal of intracranial tumor, the patient regained consciousness and discharged from the hospital in a relatively good health.