Factors that have been shown to affect outcome after acute subdural hematoma (ASDH) include age, Injury Severity Score (ISS), intracranial pressure (ICP), direct admission to a trauma center, presence of subarachnoid hemorrhage, score on the Glasgow Coma Scale (GCS), and timing of operation. However, these data come from selected patient populations (e.g., operated, comatose, or minimally symptomatic patients, etc.). In an effort to evaluate factors that predict outcome for the entire spectrum of ASDH patients, we evaluated 211 patients with ASDH and GCS scores of 3 to 15. One hundred twenty-eight patients (61%) were managed nonoperatively (Nonop), whereas 83 (39%) were managed with craniotomy [operatively (Op)]. Op patients had more severe brain injuries, as evidenced by their lower GCS scores (Op 7.8 vs. Nonop 10.7, p = 0.0001), higher incidence of large ASDH with midline shift (Op 61% large ASDH, 83% midline shift vs. Nonop 16% large ASDH, 30% midline shift, p = 0.001 for each comparison), and higher incidence of basilar cistern effacement (Op 61% vs. Nonop 21%, p = 0.001). Thirty-five percent of the Op patients had their hematoma evacuated within 4 hours (early), whereas 65% did not (delayed). Early Op patients had a significantly lower incidence of functional survival (early = 24% vs. delayed = 51%, p = 0.02). The early patients seem to have had more significant head injuries, as evidenced by their lower GCS scores (early = 7.0 vs. delayed = 8.4), higher incidence of associated intracranial injuries (early = 1.14 vs. delayed = 0.85), and higher incidence of cistern effacement (early = 76% vs. delayed = 53%, p = 0.002).(ABSTRACT TRUNCATED AT 250 WORDS)