【Introduction】Neuroprotection studies have demonstrated that mild hypothermia is helpful in reducing hypoxic/ischemic brain injury such as may occur during neonatal cardiac surgery. However traditional intensive care practice emphasizes aggressive rewarming and the risk of excessive bleeding associated with hypothermia.【Methods】Prospective collection of blood loss and temperature data from 47 neonates (3.6 + 0.09 kg, 6.4 + 0.5 days) undergoing a neonatal arterial switch procedure. Statistical analysis by multiple stepwise linear regression analysis as well as direct comparison of a hypothermic group of 26 patients with mean temp < 35.5 for first 6 hours after surgery with 21 normothermic patients.【Results】Mean total blood loss in the first 24 hours was 61.1 + 5.5 cc. Patients in the hypothermic group were less likely to have a VSD but were more likely to have been intubated and catheterized preop. There were no differences in any bypass variables. There were no differences in blood loss though by regression analysis body weight (x 16.9 cc), open chest (n = 6, + 53 cc) and lower temperature (1°C x 13.4 cc) influenced blood loss.【Conclusion】Mild postoperative hypothermia, which may be helpful in reducing neurological injury, is not associated with clinically important increase in postoperative blood loss in neonates.