Obstetric brachial plexus lesions (OBPLs) are typically caused by traction to the brachial plexus during labor. The incidence of OBPL is about 2 per 1000 births. Most commonly, the C5 and C6 spinal nerves are affected. The prognosis is generally considered to be good, but the percentage of children who have residual deficits may be as high as 20% to 30%. Surgery should be restricted to severe cases in which spontaneous restoration of function is not likely to occur (ie, in neurotmesis or root avulsions). In this article, the authors present an overview of our current understanding of the neuropathophysiology of OBPLs. The studies of preoperative electromyographic and intraoperative nerve action potential and compound motor action potentials, and of results of nerve surgery, of which some parts have been published, are discussed.