Background: Myofascial pain syndrome (MPS) is a musculoskeletal disorder, that results from trigger points, which are small, taut skeletal muscle and fascia. Objective: To compare the efficacy of Extracorporeal Shock Wave Therapy (ESWT) versus corticosteroid injection in the treatment of patients with MPS of the upper trapezius muscle. Patients and Methods:Thisprospective randomized study included fifty patients with MPS who were randomly divided equally into two groups. The active myofascial trigger points (MTrPs) in the upper trapezius were identified. Group 1 patients received ESWT 3 times at one-week intervals and group 2 patients received one injection of corticosteroids. The visual analog scale (VAS), Neck Disability Index (NDI), and pain pressure threshold (PPT) assessed the outcomes. Results:VAS scores were 7.24±1.01, 3.72 ±1.43 and 2.44±1.36 at baseline, week-4 and -8 respectively in group1; while were 7.16±1.03, 5.76 ±1.16 and 5.24±1.48 at baseline, week-4 and -8 respectively in group2. NDI scores were 11±2.63, 7.92±2.63 and 6.52±2.66 at baseline, week-4, and -8 respectively in group1, whereas were 11.16±2.36, 8.72±2.37 and 7.64±2.66 at baseline, week-4 and -8 respectively in group2. PPT scores were 2.81±0.70 at baseline, and 4.64 ±1.03 and 5.54±1.1 at week-4 and week-8 in group1, while, in group2 the scores were 2.89±0.71, 3.92 ±0.81 and 4.08±0.92 at baseline and week-4 and -8 respectively. VAS, NDI, and PPT pre- and post-treatment results showed statistically significant improvements in both groups, P <0.001. Conclusion: ESWT and corticosteroid injection considerably reduced pain intensity, physical impairment, and MTrP sensitivity to pressure in patients with MPS. ESWT was more effective in the reduction of pain and MTrPs sensitivity to pressure.