This stndy comprising six separate papers, is concerned with the techniques of, and bevaluation of arthroscopy as a diagnostic and therapeutic tool in different pathologic conditions in the upper extremity.Arthroscopy proved to increase diagnostic accuracy in 177 examined patients with anterior shoulder instability or shoulder pain. Previously not well described patterns of pathological morphology in the ventral joint capsule after anterior shoulder dislocations were disclosed. A new classification system of rotator cuff pathology to be used for arthroscopy in the subacromial impingement syndrome is suggested. Different stages of rotator cuff pathology were found to influence the clinical results after arthroscopic acromioplasty in 79 patients.An anatomical stndy on 16 cadaver elbows revealed the close proximity between commonly used arthroscopic portals and important neurovascular structures. The usefulness and potential risks of each portal were demonstrated and a preferred procedure for diagnostic elbow arthroscopy was suggested.Wrist arthroscopy was performed in 30 patients with long-standing post-traumatic pain and resulted in increased diagnostic accuracy. In patients where clinical examination and radiography had shown no abnormality, arthroscopy demonstrated serious carpal ligament injuries and related instability.A technique for arthroscopic wrist synovectomy was described in patients with rheumatoid arthritis. In 18 wrists of 16 patients, a reasonably radical synovectomy could be achieved with this atraumatic method. Primary results showed decreased pain and increased grip-strength in all patients and an increased range of motion in some.