Direct and indirect trauma can cause injury to various portions of the pectoralis major muscle in varying degrees. Sprains and partial tears of the pectoralis major muscle are not uncommon. Surgical repair in acute injuries can often produce excellent results in selected patients. Complete injuries of the muscle tendon itself (Type IIID) are best treated with surgical repair in otherwise healthy patients. Delayed diagnosis and delayed repair may prevent excellent results. A functional classification as presented here can aid in the diagnosis and treatment of these injuries.