Examination at 18 months post-term of 139 infants of birth weight less than or equal to 1,500 gm revealed 18 instances (13%) of persistent median nerve damage. All affected infants had received frequent percutaneous brachial artery punctures as neonates. Block sections of the cubital fossa done at autopsy on 12 randomly selected very low-birth-weight infants showed perineural hemorrhage, and Wallerian degeneration or traumatic neuroma of the median nerve in eight patients. It is recommended that brachial artery punctures be avoided whenever possible in the neonatal period.