The aim of this clinical trial was to evaluate the effectiveness of therapeutic MD on pain, functional capacity, muscle strength, quality of life, and depression in patients with subacromial impingement syndrome (SIS). A total of 40 inpatient subjects with definite SIS were included in this study. These patients were sequentially randomized into 2 groups. Group 1 (n = 20) received therapeutic MD. Group 2 (n = 20) was served as control group and received sham MD. Superficial heat and exercise program were given to both groups. Both of the programs were performed 5 times weekly for 3 weeks. Patients were assessed before treatment (BT), after treatment (AT), and at a 1-month follow-up (F). Outcome measures included visual analogue scale, goniometry, Shoulder Pain and Disability Index, Shoulder Disability Questionnaire, shoulder isokinetic muscle testing, handgrip strength, Short Form 36, and Beck Depression Index. The patients with SIS in each group had significant improvements in pain, shoulder ROM, disability, shoulder muscles and grip strength, quality of life, and depression AT and F when compared with their initial status (P < 0.05). There was no statistically significant difference between the groups according to all the parameters regarding the change scores between AT-BT test and F-BT test (P > 0.05). A 2,450-MHz MD regimen showed no beneficial effects in patients with SIS, so the superficial heat and exercise program, as it is efficient, may be preferable for the treatment of SIS, alone.