Arthroscopy has served a diagnostic role for most of this century, but found widespread popularity only when operative interventions were coupled with the procedure. The untapped potential inherent in directly observing the pathoanatomy underlying various rheumatologic disorders is being unlocked by developments on several fronts that have taken arthroscopy away from the operating room environment. Information from arthroscopy can influence diagnosis and treatment in certain non-traumatic knee disorders, particularly when the cause of synovitis is not evident from other clinical features and when knee symptoms are accompanied by bland synovial fluid and X-rays that are normal or show only minimal changes of osteoarthritis. Other joints can now be arthroscoped, which may prove useful for rheumatological diagnosis and evaluation, particularly for the smaller joints of the upper extremity commonly affected in 'early' disease states.