Reports prior to 1980 describe overall mortality rates for acute subdural hematomas (SDH's) ranging from 40% to 90% with poor outcomes observed in all age groups. Recently, improved results have been reported with rapid diagnosis and surgical treatment. A relatively large number of older patients (34 patients over 65 years old) were treated recently at Harborview Medical Center, enabling a retrospective comparison with similarly treated younger patients (33 patients aged 18 to 40 years). Clinical information and computerized tomography morphometric data were obtained. Patients in the younger group were most often injured in motor-vehicle accidents (15 cases), whereas falls were most frequent in the older group (19 cases). Patients in both groups were rapidly resuscitated in the field; more than 30% were treated within 1 hour after the time of injury. Injury severity, determined by the admission Glasgow Coma Scale score, was similar for the two groups. Mean acute SDH volume was significantly larger in the older patients than in the younger group (mean +/- standard deviation: 96.2 +/- 117.2 vs. 21.6 + 27.7 cu cm), as was the amount of midline shift (1.2 +/- 1.69 vs. 0.6 +/- 0.75 cm). Surgical treatments were similar, but outcomes were dramatically different for the younger and older patients. Mortality rates were more than four times higher in older patients than in younger ones (74% vs. 18%). Three older patients and 25 younger patients were functional survivors. Old age, a larger SDH volume, and a larger midline shift all correlated with a poor outcome. The results of this study suggest that the pathophysiology of acute SDH varies with age, and that currently employed resuscitation and treatment methods have differentially improved the outcome for younger patients.