210 patients with shoulder impingement syndrome were randomized to one of three treatment groups: arthroscopic subacromial decompression, diagnostic arthroscopy (sham surgery), or an exercise therapy program. Primary outcomes were pain at rest and pain during activity, and follow-up was performed over 24 months. Analyses demonstrated no statistically significant differences in pain scores between the arthroscopic subacromial decompression group and the diagnostic arthroscopy group. Additionally, while statistically significant lower pain scores were noted in the arthroscopic subacromial decompression group compared to the exercise therapy group, the differences were reported to not be clinically relevant.