The authors analyzed the clinicoradiological presentation of traumatic basal ganglia hematomas (TBGHs) in severely head injured (SHI) patients. The records of 37 patients (28 male and nine female patients with a mean age of 28 years) in whom computerized tomography (CT) scans revealed TBGHs 2 ml or more in volume were retrospectively reviewed. These cases represented 2.4% of the total series of 1526 SHI patients admitted to the authors' institution between 1979 and 1998. Thirty-five patients (94%) were involved in traffic accidents and only two exhibited a period of lucidity. Associated extracranial injuries were seen in 21 patients (57%) and coagulation disorders in 32 (86%). Skull fracture was present in 10 (43%) of the 23 patients in whom skull x-ray films were obtained. Computerized tomography findings indicated diffuse axonal injury in 27 patients (73%), intraventricular hemorrhage in 22 patients (59%), and subarachnoid hemorrhage in 16 patients (43%). In all but two patients, the TBGHs were visible on the initial CT scan, and in 28 cases (76%) these hematomas were contralateral to the side of impact. Hematoma enlargement over the first few posttraumatic days was noted in 65% of the patients in whom control CT scans had been obtained (22 of 34 patients). Four patients (11%) underwent surgery to remove their TBGHs. Final outcomes were poor: 22 patients (59%) died, two (5%) became vegetative, seven (19%) experienced severe disabilities, and only six patients (16%) made a favorable recovery. Traumatic basal ganglia hematomas are dynamic lesions that tend to enlarge during the acute posttraumatic period. The overall prognosis in this series was poor. Patients in whom the volume of the hematoma was larger than 25 ml and those in whom hematoma volume enlargement or raised intracranial pressure occurred had the worst outcomes, perhaps indicating the need for a more aggressive surgical treatment.