Background: Severe neonatal encephalopathy (NE) of hypoxic-ischaemic origin may cause death or life-long disability. Acute encephalopathy may also affect cerebrovascular control. Pourcelot's cerebrovascular resistance index (RI) ≤0.55 was predictive of poor outcome in normothermic NE infants. Recent studies have questioned its predictive power during therapeutic hypothermia (HT). Objective: To assess the predictive power of RI during HT and after rewarming. Methods: 45 infants with NE treated with HT for 72 h had their RI calculated during early (median 11 h) and late (median 62 h) cooling and after rewarming (median 89 h). Poor outcome was defined as death or abnormalities on day 10 magnetic resonance imaging shown to predict severe neuromotor disability. Results: RI ≤0.55 during cooling did not differentiate between good and poor outcome (late cooling, p = 0.08), but was powerful after rewarming (p = 0.004). RI ≤0.55 predicted true poor outcome in 43% (95% confidence interval (CI): 12, 80) during late cooling and in 100% (95% CI: 31, 100) after rewarming. RI >0.55 predicted good outcome in 86% (95% CI: 69, 95) during late cooling and in 89% (95% CI: 74, 96) after rewarming. Conclusions: Low RI is not predictive of poor outcome during HT in NE infants, but regains the predictive power seen in normothermic infants after rewarming. © 2014 S. Karger AG, Basel.