Study Design: Randomized clinical trial. Background: Shoulder pain is a common musculoskeletal disorder encountered by physical therapists with as much as 44% of shoulder pain attributed to subacromial pain syndrome (SPS). Thoracic spine thrust manipulation (TSTM) has been reported to be effective in the short-term for improving pain and function in individuals with SPS, but the mechanisms of this remain elusive. Furthermore, it is unknown whether individuals with SPS respond differently based on the TSTM technique received. Objectives: The purpose of this study was to compare the immediate effects of a supine TSTM, seated TSTM, and sham manipulation on the primary outcomes of self-reported pain, function, and satisfaction and secondary biomechanical impairments examined in individuals with SPS. Methods: Sujects were randomized to receive a seated TSTM (n=20), supine TSTM (n=20), or sham manipulation (n=20). The primary outcomes of self-reported pain, function, and satisfaction were measured through the Penn Shoulder Score. Secondary outcomes were changes in scapular upward rotation and posterior tilt, peak force generated in tests for the middle trapezius, lower trapezius, and serratus anterior, and pectoralis minor muscle length. Impairment measures were immediately reassessed and the Penn Shoulder Score was reassessed at 48 hours. Results: There were no significant between group differences in immediate or short-term follow-up outcomes. Conclusions: Two TSTM techniques resulted in no differences in pain, satisfaction and function when compared to a sham. TSTM does not appear to have an immediate effect on the scapular impairments examined. Level of Evidence: Therapy, level 1.