The differential diagnosis includes a variety of intrinsic musculoskeletal disorders, and individual patients may exhibit considerable overlap in their symptoms manifesting a combination of specific conditions. Impingement syndrome is a term that has been adopted to encompass many painful shoulder syndromes that result most frequently from repetitive overhead use of the arm. The pathologic entities included in this syndrome are subacromial tendonitis and bursitis, supraspinatus tendonitis, rotator cuff tendonitis, and the painful arc syndrome. Impingement syndrome is a painful overuse condition characterized by positive findings with impingement testing and relief of pain with anesthetic injection of the subacromial space. Subacromial bursitis is generally seen in patients younger than 25 years and will present with positive impingement tests with different degrees of tenderness at the lateral proximal humerus or in the subacromial space. Rotator cuff tendonitis is distinguished by an incidence primarily in individuals 25 to 40 years of age and findings of tenderness of the rotator cuff with mild to moderate muscular weakness. In more chronic disease, crepitus, decreased range of motion, and osteophyte formation visible on plain radiograph also may be apparent. Rotator cuff tears occur primarily in patients older than 40 years and are associated with muscular weakness (especially with abduction and external rotation) and cuff tenderness. Ninety percent will be chronic tears with a history of minimal or no trauma; in severe disease, muscular atrophy may be present. Acute tears may occur in patients of any age and result from significant force producing a tearing sensation with immediate pain and disability. In patients between the ages of 30 and 50 years, abnormal calcifications on radiograph in the clinical setting of a painful shoulder with rotator cuff tenderness and often crepitus suggest the diagnosis of calcific tendonitis. Osteoarthritis is characteristically associated with degenerative disease in other joints (primary) or previous fracture or other underlying disorder (secondary). The hallmark of adhesive capsulitis is significantly painful and limited range of motion often, but not always, associated with a period of immobilization. Radiographs should be obtained to exclude posterior glenohumeral dislocation.