OBJECTIVE: To investigate the short-term effects of thoracic spine manipulation (TSM) on pain, function, scapular kinematics, and scapular muscle activity in individuals with shoulder impingement syndrome. DESIGN: Randomized controlled trial with blinded assessor and patient. SETTING: Laboratory. PARTICIPANTS: Patients with shoulder impingement syndrome (N=61). INTERVENTIONS: Participants were randomly allocated to TSM group (n=30) or sham-TSM group (n=31) and attended 2 intervention sessions over a 1-week period. MAIN OUTCOME MEASURES: Scapular kinematics and muscle activity were measured at day 1 (baseline, before the first intervention), day 2 preintervention (before second intervention), day 2 postintervention (after the second intervention), and day 3 (follow-up). Shoulder pain and function were assessed by the Disability of the Arm, Shoulder and Hand questionnaire and Western Ontario Rotator Cuff Index at baseline, day 2 preintervention, and follow-up. An assessor blinded to group assignment measured all outcomes. RESULTS: Pain decreased by 0.7 points (95% confidence interval, 1.3-0.1 points) at day 2 preintervention and 0.9 points (95% confidence interval, 1.5-0.3 points) at day 2 postintervention in the TSM group. The Disability of the Arm, Shoulder and Hand questionnaire (P=.01) and Western Ontario Rotator Cuff Index (P=.02) scores improved in both groups. Scapular upward rotation increased during arm lowering (P<.01) at day 2 postintervention (5.3 degrees ) and follow-up (3.5 degrees ) in the TSM group. Upper trapezius activity increased (P<.05) in the sham-TSM group. Middle trapezius, lower trapezius, and serratus anterior decreased activities in both groups during elevation and lowering of the arm. CONCLUSIONS: TSM may increase scapular upward rotation during arm lowering. TSM does not seem to influence activity of the scapular muscles. The results concerning shoulder pain, function, scapular tilt, and internal rotation are not conclusive. CI - Copyright (c) 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.