OBJECTIVE: The Brain Trauma Foundation published "Guidelines for the Management of Severe Head Injury" in 1996. These evidence based clinical guidelines (CGs) recommended against prophylactic hyperventilation and glucocorticoid use, and advocated for blood pressure (BP) resuscitation, and the careful use of mannitol in the event of elevated intracranial pressure (ICP). We sought to measure the penetrance of these guidelines into the practice patterns of Michigan emergency physicians (MEPs). METHODS: An anonymous mail survey was sent to all 566 MEPs who are members of the American College of Emergency Physicians. Three patients with severe head injury were presented, all with Glasgow Coma Scores (GCSs) of 8 or less. The physicians were asked to choose from 15 diagnostic and treatment options, which included: intubation and hyperventilation, BP resuscitation, IV mannitol administration, and IV glucocorticoid administration. RESULTS: 319 (56%) surveys were returned. 46% (95% CI = 40% to 51%) of MEPs elected to inappropriately use prophylactic hyperventilation, 78% (95% CI = 75% to 81%) did correct hypotension with systolic BP < 90 mm Hg. 83% (95% CI = 80% to 86%) administered mannitol appropriately. Very few MEPs administered IV glucocorticoids. CONCLUSIONS: Despite being published nearly 4 year ago, the "Guidelines for the Management of Severe Head Injury" have not been uniformly incorporated into the practice patterns of MEPs. Specifically, many physicians continue to rely on prophylactic hyperventilation despite strong recommendations against its use.