Our purpose was to determine the intratester and intertester reliability of measurements of both scapular and glenohumeral rotation during active arm elevation in the scapular plane with a new device, the scapulohumeral goniometer (SHG). Ten physical therapists, with 1 to 29 years of clinical experience, obtained repeated measurements on 45 subjects who were 27 to 82 years old. All subjects were tested in uniform standing position with the handheld SHG, which was positioned over the subject's scapula and posterior shoulder according to operationally defined landmarks. For both scapular and glenohumeral rotation, 50% of the time the first and second measurements made on a patient by the same physical therapist differed by 3° or more. Ten percent of the time, these measurements differed by 8° or more. Measurements of active range of movement of scapular and glenohumeral rotation made by the same physical therapist during arm elevation in the scapular plane are clinically unacceptable when obtained with the current techniques for positioning the SHG. Clinical decisions based on results of active scapular and humeral motion in the scapular plane as measured on a patient by the same therapist with an SHG should be made with caution, because of the variability associated with this procedure.