120 patients with a clinical diagnosis of subacromial impingement syndrome who underwent conventional therapy participated in this study to determine the effectiveness of diacutaneous fibrolysis on pain, function, active range of motion and patient perceived improvement. All patients participated in conventional physiotherapy and were randomized into an intervention group which received additional diacutaneous fibrolysis, a placebo group that underwent a sham treatment and a control group. All three groups improved significantly in pain and function, suggesting that patients can benefit from conventional physiotherapy. The patients who were administered diacutaneous fibrolysis experienced the best overall results immediately following treatment and better perceived improvement compared to the control group.