Parsonage-Turner syndrome (PTS) is a rare neurological disorder characterized by severe unilateral pain in the shoulder. Muscle weakness and wasting can be also observed. The etiology is unknown. The study presents the case of a 15-year-old male with increasing paresis of the right upper limb. The patient reported pain and dizziness. Romberg's test and finger-to-nose test were positive. There was an abduction disorder of the right glenohumeral joint. MRI showed the cerebellar vermis with a slightly increased intensity. After starting the treatment, the cerebellar symptoms disappeared quickly, but the problems with the shoulder persisted. An ultrasound of the right brachial plexus showed oedema lesions. EMG revealed signs of damage to the right brachial plexus. Rehabilitation was recommended. After 10 months, the boy's clinical condition improved. PTS is a disease that presents great diagnostic difficulties. Doctors must take this syndrome in the differential diagnosis of shoulder pain.