A 1-month-old infant was referred for a rapidly expanding mass at the left elbow. Angiography showed contrast extra-vasation from the brachial artery in a 4 X 3 cm pseudo-aneurysm. This false aneurysm was treated surgically with good result. It is probable that accidental arterial puncture during repeated veni punctures in the neonatal period for determination of bilirubinaemia was responsible for pseudo-aneurysm of the brachial artery.