Rationale:Pes anserine (PA) bursitis is an inflammatory condition of the medial knee. The PA bursa becomes more painful when infected, damaged, or irritated. Although various treatment options have been attempted to treat PA bursitis, optimal treatments are still debated. This study aims to investigate the effect of polydeoxyribonucleotide (PDRN) injection on reducing pain and inflammation in a patient presenting with PA bursitis.Patient concerns:A 50-year-old female patient was admitted to our pain clinic with symptoms of tenderness and pain over the medial knee. Physical examination revealed the pain to be located over the proximal medial tibia at the insertion of the conjoined tendons of the PA. The knee had lost its range of movement and strength, and resisted knee flexion.Diagnoses:She was diagnosed as having PA bursitis.Interventions:Ultrasound guided PA bursa injection was carried out.Outcomes:Follow-up for the patient was more than eight months. She showed good improvement in PA bursitis without any complications.Lessons:This is the first successful report of successful PDRN injection for PA bursa.