BACKGROUND Piriformis syndrome (PS) is the common entrapment neuropathy causing buttock pain. Patients are conventionally treated with lifestyle modification, exercise, non-steroidal anti-inflammatory drugs, corticosteroid or botulinum toxin injections. However, some patients may not respond to these conventional treatment methods. Platelet rich plasma (PRP) injection has been shown to be beneficial in various muscular injuries, but its effects have not yet been investigated in PS. OBJECTIVE The aim of this study was to explore the effect of PRP on pain and functional status in patients with PS, and to identify any correlations between clinical changes and demographic features. METHODS A total of 60 patients with PS were randomly separated into two groups (PRP and control groups). All patients received one session of either PRP or saline injection performed under ultrasound guidance. The pain was measured with a visual analog scale (VAS) and Oswestry Disability Index (ODI) scores were noted at three intervals in both groups: before treatment, 1 week after treatment and 1 month after treatment. RESULTS The VAS and ODI scores were improved in both groups. The improvement was more obvious in the PRP group in the first week, and the results were similar for both groups when measured 1 month after the treatment. CONCLUSIONS Ultrasound-guided PRP injection provided greater improvements in both pain and functional status in patients with PS, starting in the early period after treatment. A repeat injection might be needed for a long-term effect.