Acute compartment syndrome can have disastrous consequences. Because unusual pain may be the only symptom of an impending problem, a high index of suspicion, accurate evaluation, and prophylactic treatment will allow the physician to intervene in a timely manner and prevent irreversible damage. Muscles tolerate 4 hours of ischemia well, but by 6 hours the result is uncertain; after 8 hours, the damage is irreversible. Ischemic injury begins when tissue pressure is 10 to 20 mm Hg below diastolic pressure. Therefore, fasciotomy generally should be done when tissue pressure rises past 20 mm Hg below diastolic pressure.