Objective To investigate the effectiveness of thermal and sub-thermal capacitive-resistive monopolar radiofrequency at 448 kHz plus exercising compared to sham radiofrequency plus exercising on pain, functionality, and quality of life in patients with subacromial pain. Design Randomized, controlled, parallel, double-blind, three-arm clinical trial. Setting Hospital and Primary Care. Subjects Eighty-one participants with subacromial pain in three intervention groups. Interventions Three interventions with capacitive-resistive radiofrequency (thermal, sub-thermal, and sham) over 9 sessions (3 per week) plus an exercising protocol identical for all groups over 15 sessions (5 per week). Outcome measures Visual analogue scale and pressure pain threshold for pain, Shoulder Pain and Disability Index and Quick-Disabilities of the Arm, Shoulder and Hand for functionality, and quality of life via the European Quality of Life-Five Dimensions were assessed at baseline, immediately posttreatment, and 1 month and 3 months post-intervention. Results No between-group differences were found in the pain visual analogue scale (F = 1.0; P = 0.37), Shoulder Pain and Disability Index (F = 1.0; P = 0.36), European Quality of Life-Five Dimensions (F = 0.76; P = 0.47), and pressure pain (F = 0.14; P = 0.86) outcomes, with a statistical power < 0.30 for all comparisons. Between-group differences were found in the Quick-Disabilities of the Arm, Shoulder and Hand (F = 3.4; P < 0.038), with an improvement of −14.1 points (confidence interval at 95% (95% CI) −28.1 to −0.1) in the thermal versus the sham group at 1 month follow-up. The mobility dimension of European Quality of Life-Five Dimensions improved in a greater proportion of participants in the thermal group (22.2% thermal, 7.4% sub-thermal, and 0.0% sham; P = 0.02) Conclusion Adding thermal radiofrequency to exercising can further improve slightly functionality and mobility in people with subacromial pain in the short term, but not pain perception. Future studies with larger sample sizes are warranted to increase statistical power.