The purpose of this study was to analyze the outcomes of arthroscopic coracoplasty in the treatment of subcoracoid impingement syndrome. We compared 23 shoulders that underwent arthroscopic coracoplasty for the treatment of subcoracoid impingement syndrome with 28 shoulders that did not undergo arthroscopic coracoplasty for the treatment of subcoracoid impingement syndrome, which comprised the control group. All the shoulders had subcoracoid and subacromial impingement syndrome with or without rotator cuff tear. Subcoracoid impingement was defined as a coracohumeral distance of less than 6 mm on the preoperative magnetic resonance image with anterior shoulder pain or tenderness. The 2 groups were further divided into several subgroups according to the size of concomitant rotator cuff tear, and a comparative analysis of functional outcomes after surgery among the subgroups was performed. In the 2 groups, the overall functional outcomes improved after surgery. The study group showed a significant increase in internal rotation compared with that in the control group (P = .001) at the last follow-up. The large to massive rotator cuff tear subgroup of the study group showed a significant increase in internal rotation (P = .017). On the other hand, no significant difference was seen in the subgroups with small to medium rotator cuff tears including isolated subscapularis tears. The no rotator cuff tear subgroup of the study group showed a significant increase in internal rotation (P = .046). Arthroscopic coracoplasty for subcoracoid impingement syndrome can provide a satisfactory outcome. In particular, a significant increase in internal rotation of the treated group was achieved after surgery in comparison with the untreated group, especially in the large to massive rotator cuff tear subgroup and in the no rotator cuff tear subgroup. Level III, retrospective comparative study.