Over a six-year period, 166 shoulder arthroscopies were performed in 153 patients with symptoms of subluxation, but no firm evidence of dislocation and no clear-cut clinical diagnosis. Arthroscopy confirmed the working diagnosis in 133 shoulders (80%), but changed it in 33 (20%). In 26 shoulders the presumed direction of instability was changed and in seven a different diagnosis was made. Arthroscopy was particularly helpful for patients with shoulder instability of uncertain type or direction.