Chronic accumulation of blood in the subdural space, most frequently occurring over the lateral and superior aspects of a cerebral hemisphere. Clinical manifestations may be delayed for days to weeks, when affected individuals may present with confusion, drowsiness, hemiparesis, ATAXIA; APHASIA; and other signs of neurologic dysfunction. The condition tends to occur after the age of 50 years. It may be spontaneous, follow $CRANIOCEREBRAL TRAUMA$, or occur in association with bleeding disorders, the use of anticoagulant medication, locally invasive tumors, and other disorders. (From Adams et al., Principles of Neurology, 6th ed, p887).