Two newborn infants had isolated radial nerve lesion documented on electromyography. Fibrillation potentials present in one child at age 6 days suggest the possibility of an in utero onset. Skin necrosis present above the triceps muscle and radial nerve favors an entrapment mechanism, possibly from the umbilical cord. Because both patients had complete resolution in 4 months, it is important to differentiate this lesion from the more common but more serious medial brachial plexus lesion.