The prospective study reported here evaluated the relationship between coagulopathy, catecholamines, and outcome in severe head trauma. Thirty-six trauma patients (10 with penetrating injuries, 26 with blunt injuries, 50% overall mortality) were evaluated. These patients had severe head trauma (Glasgow Coma Scale score less than 9). Blood was analyzed for platelet count, prothrombin time (PT), partial thromboplastin time (PTT), and fibrinogen, D-dimer, antithrombin III, protein C, and protein S levels. A 24-hour urine sample was collected for vanillylmandelic acid (VMA), normetanephrine, and metanephrine determinations. A control group of five patients undergoing elective neurosurgery was also studied. Statistically significant differences between head injury survivors and nonsurvivors were present for platelet count, PT, and fibrinogen activity. There were no differences in the results of the other coagulation tests or in urinary catecholamine levels. The trauma patients differed from the elective neurosurgery patients with regard to D-dimer levels, PT, PTT, protein C levels, and urinary normetanephrine concentrations. Head trauma patients have a coagulopathy that is absent in patients following elective neurosurgical procedures. The coagulopathy may correlate with poor survival in head trauma and may be related to a catecholamine surge.