At her second day of life, a 2,200 g, 34 weeks gestational age female newborn infant with idiopathic respiratory distress syndrome, under treatment with mechanical ventilation and monitored through an umbilical arterial catheter (UAC), had severe clinical signs of arterial obstruction of her left limb. Signs of occlusion at the common femoral artery level were evident at Doppler ultrasonography. Doppler determinations showed early arterial blood flow improvement before amelioration of skin coloration and arterial pulses, that allowed close observation and withholding of surgical treatment which was finally not necessary. Eighteen newborn babies with an umbilical arterial catheter were then prospectively followed by Doppler ultrasound flow determinations. No further cases with clinical signs of arterial occlusion were found and Doppler studies performed in these late cases showed normal results in all of them. Doppler ultrasound flow determination is helpful for the diagnosis and management of lower limb arterial obstruction in newborn infants with umbilical arterial catheters.