Mark L. Prasarn, MD and Elizabeth A. Ouellette, MD J Am Acad Orthop Surg, Vol 19, No 1, January 2011, Acute compartment syndrome occurs when pressure within a fibro-osseous space increases to a level that results in a decreased perfusion gradient across tissue capillary beds. Compartment syndromes of the hand, forearm, and upper arm can result in tissue necrosis, which can lead to devastating loss of function. The etiology of acute compartment syndrome in the upper extremity is diverse, and a high index of suspicion must be maintained. Pain out of proportion to injury is the most reliable early symptom of impending compartment syndrome. Diagnosis is particularly difficult in obtunded patients and in young children. Early recognition and expeditious surgical treatment are essential to obtain a good clinical outcome and prevent permanent disability.