Peroneal neuropathy presenting at birth is a rare disorder. Although neonatal mononeuropathies may be related to obstetrical complications, prenatal mechanisms should be also considered. We describe an infant who was born at term by cesarean section due to breech presentation with a unilateral footdrop. Lack of compound muscle action potential in the peroneal nerve and denervation potentials confined to the tibialis anterior and the extensor hallucis longus muscles in the electrophysiological studies on the fourth day of life strongly suggest an isolated peroneal neuropathy of intrauterine onset. Early and sequential electrodiagnostic studies will be important to provide better temporal and pathophysiologic definitions, the better timing of onset and prognosis for mononeuropathies presenting in newborn infants.