Objectives: In this study, we aimed to investigate the effectiveness of intra-articular platelet-rich plasma (PRP) injection in adhesive capsulitis. Patients and methods: Between January 2019 and December 2019, a total of 40 patients (21 males, 19 females; mean age: 57.1±6.5 years; range, 44 to 72 years) with idiopathic adhesive capsulitis were included. The patients were randomly assigned into two equal groups as the PRP and the control group. The PRP group received two doses of PRP via intra-articular route biweekly under ultrasound guidance. No injection was performed to the control group. In both groups, stretching and Codman exercises were applied as a home- based program. The Visual Analog Scale (VAS), range of motion (ROM), and Shoulder Pain and Disability Index (SPADI) scores were evaluated before the treatment and at 2, 6 and 12 weeks after the treatment. Results: There were significant differences in all VAS, SPADI, and ROM scores at all time points after treatment compared to baseline in both groups. At the end of the study, there were significant differences in the active flexion, passive flexion, active abduction, passive abduction, and active external rotation scores at 12 weeks between the groups (p=0.012, p=0.015, p=0.008, p=0.019, and p=0.040, respectively). No significant difference was observed between the groups in terms of VAS and SPADI scores and the other parameters (active and passive extension, active and passive internal rotation, passive external rotation) at 2, 6, and 12 weeks (p>0.05). Conclusion: The addition of PRP to exercise treatment can improve patients' joint mobility, but not pain and disability in patients with adhesive capsulitis.