Upper extremity arterial injuries in preterm infants are usually of iatrogenic origin. Current microsurgical techniques permit extremity revascularization in these patients. The authors report the microsurgical repair of a 0.7-mm brachial artery in a 940-g preterm infant. The preterm infant warrants special consideration due to physiological immaturity. Rapid fluid shifts, a relative polycythemia, and the potential for low cardiac output states increase the risk for vascular thrombosis. Systemic heparinization is contraindicated in this population due to the risk of intraventricular hemorrhage. Optimization of various physiological variables should reduce the risk of thrombosis.