Brachial neuritis is a rare disorder of unknown etiology that causes pain and weakness of the shoulder and upper extremity. There have been many descriptions of the disorder in the literature. The classic symptoms begin with an acute onset of sharp pain in the shoulder girdle. As the pain subsides, weakness occurs. The diagnosis often is difficult to make in the acute setting. Diagnostic tests typically are not helpful, although electromyography may be useful. The treatment is chiefly supportive with analgesics initially followed by range of motion exercises. Full functional recovery is expected in most patients, although the interval may be protracted. Understanding the disorder of brachial neuritis and its course will assist in the diagnosis and treatment.