Obstetric brachial plexus palsy (OBPP) is caused by traction to the brachial plexus during labour. In the majority of cases delivery of the upper shoulder is blocked by the mother's pubic symphysis (shoulder dystocia). If additional traction is applied to the child's head, the angle between the neck and the shoulder is forcefully widened, overstretching the ipsilateral brachial plexus. The resulting traction injury may vary from neurapraxia or axonotmesis to neurotmesis and avulsion of rootlets from the spinal cord. Recently, the exact origin of OBPP was again a matter of debate. It was suggested that intrauterine maladaptation, not nerve traction, causes the plexopathy. The incidence of OBPP varies from 1.6 to 2.9 per 1000 births in prospective studies. The upper brachial plexus is most commonly affected, resulting in paresis of the shoulder and biceps muscles, as first described by Erb and Duchenne. Hand function is additionally impaired in approximately 15% of patients; isolated injury to the lower plexus (Déjèrine-Klumpke's type) is rare.