There are many measurement tools for assessing patients’ shoulder symptoms (pain) and function (what patients can do), but they do not measure activity (how often a patient engages in activity). This is relevant because activity level can have an important impact on a patient’s outcome. Our goal was to develop a short, easy to administer measure of shoul- der activity which could be used to predict outcome of shoul- der disorders. The activity scale was developed using estab- lished principles: item generation, item reduction, pretesting, and reliability and validity testing. The activity rating is a numerical sum of scores for five activities rated on a five- point frequency scale from never performed (0 points) to daily (4 points). Patients were scored on the following crite- ria: carrying an object 8 lb or heavier by hand, handling objects overhead, weight training with arms, swinging mo- tion (ie, hitting tennis or golf ball), and lifting objects 25 lb or heavier. Two additional multiple choice questions provide a score assessing participation in contact and overhead sports. The activity scale showed excellent reliability and construct validity. It can be completed quickly and used in conjunction with patient-based measures of shoulder outcome to define patient populations for cohort studies, and to assess activity level as a prognostic factor in patients with shoulder disor- ders.