We report a 44-year-old woman with calcific tendinitis of the shoulder treated with platelet-rich plasma injection. Prior to this, she had no improvement of the symptoms after 6 weeks of ultrasound treatment, Codman exercises, and anti-inflammatory treatment. Platelet-rich plasma was injected into the subacromial area 3 times at 2-week intervals. She had progressive improvement of pain after 2 weeks, and was asymptomatic at week 6. The patient then underwent the previous protocol of rehabilitation. At the one-year follow-up, the patient was pain-free and had complete resolution of calcific tendinitis. The patient had regained full range of movement and had resumed all her activities.