Display omitted To review studies that assessed systemic hypothermia as an organ protection strategy in adults undergoing cardiac surgery with cardiopulmonary bypass. A systematic review and meta-analysis. Randomized controlled trials, irrespective of blinding, language, publication status, and date of publication, were identified by searching the Cochrane Central register of Controlled Trials, MEDLINE, and Embase until November 2020. Risk of bias assessment was performed according to Cochrane methodology. Treatment effects were expressed as risk ratios and 95% confidence intervals. Heterogeneity was expressed as I2. Systemic hypothermia. Forty-eight trials enrolling 6,690 patients were included in the analysis. Methodologic quality of the studies included was low, mostly due to insufficient allocation concealment or blinding. Random-effects meta-analysis did not resolve uncertainty as to the risks and benefits for hypothermia versus normothermia for key primary and secondary outcomes, including mortality (1.21, 0.94 to 1.56, I2 = 0%) and brain injury (0.87, 0.67 to 1.14, I2 = 0%). Sensitivity analyses restricted to trials at low risk of important bias demonstrated higher mortality with hypothermia (1.70, 1.05 to 2.75, I2 = 0%), with little or no treatment effect on brain injury (1.01, 0.69 to 1.49, I2 = 0%). There was no interaction between cardioplegia temperature and the effects of cardiopulmonary bypass temperature on outcomes. There was insufficient evidence to assess the effects of hypothermia in noncoronary artery bypass graft surgery. The existing evidence for an organ-protective effect of hypothermia in adult cardiac surgery is of low quality and inconsistent.