To determine the effects of scapular mobilization on function, pain, range of motion, and satisfaction in patients with subacromial impingement syndrome (SAIS). Design: Randomized, double-blind, placebo-controlled clinical trial. Setting: University hospital clinics in Turkey. Participants: 66 participants (mean +/- SD age 52.06 +/- 3.71 y) with SAIS. Interventions: Participants were randomized into 3 groups: scapular mobilization, sham scapular mobilization, and supervised exercise. Before the interventions transcutaneous electrical stimulation and hot pack were applied to all groups. Total intervention duration for all groups was 3 wk with a total of 9 treatment sessions. Main Outcome Measures: Shoulder function and pain intensity were primary outcome measures; range of motion and participant satisfaction were secondary outcome measures. Shoulder function was assessed with the short form of the Disabilities of the Arm, Shoulder and Hand Questionnaire (DASH). A visual analog scale was used to evaluate pain severity. Active range of motion was measured with a universal goniometer. A 7-point Likert scale was used to evaluate satisfaction. Outcome measurements were performed at baseline, before visits 5 and 10, 4 wk after visit 9, and 8 wk after visit 9. Results: There was no group difference for DASH score (P = .75), pain at rest (P = .41), pain with activity (P = .45), pain at night (P = .74), and shoulder flexion (P = .65), external rotation (P = .63), and internal rotation (P = .19). There was a significant increase in shoulder motion and function and a significant decrease in pain across time when all groups were combined (P < .001). The level of satisfaction was not significantly different for any of the questions about participant satisfaction between all groups (P > .05). Conclusion: There was not a significant advantage of scapular mobilization for shoulder function, pain, range of motion, and satisfaction compared with sham or supervised-exercise groups in patients with SAIS.