Chronic inflammation and degenerative tendonitis of the supraspinatus muscle is an important cause of intrinsic shoulder pain. Injury to this muscle is usually caused, not by a single event, but by slight to moderate trauma repeatedly to the same anatomic area. The term repetition strain injury is used to describe this form of microtrauma. Repetition strain injury of the supraspinatus muscle is not an isolated event, but rather a form of microtrauma that affects the entire shoulder girdle. This functional unit must be evaluated and considered in the treatment plan. The authors discuss the diagnosis of this pain syndrome, which is based on the patient's work history, motion and strength testing, and palpation for trigger points. They also provide instruction in treatment involving manipulation with functional and counterstrain techniques combined with home exercise and modification of work posture.