Pain involving the shoulder is a common complaint encountered by physicians working in the emergency department. The differential diagnosis includes traumatic injuries such as fractures and dislocations, overuse injuries such as tendonitis and arthritis, and referred pain from a diaphragmatic focus such as pneumonia or myocardial infarct. Infection involving the soft tissues of the shoulder is rare and, most frequently, a result of direct trauma. Pyomyositis is an infection of the muscle from a transient bacteremia and is usually caused by Staphylococcus aureus. It is most likely to occur after a muscle injury. We describe a patient with pyomyositis of the shoulder caused by an anaerobic bacterial infection of the infraspinatus muscle, which occurred after a dental extraction.