Background: Parenteral nutrition is commonly administered during therapeutic hypothermia. Randomised trials in critically ill children indicate that parenteral nutrition may be harmful., Objective: To examine the association between parenteral nutrition during therapeutic hypothermia and clinically important outcomes., Design: Retrospective, population-based cohort study using the National Neonatal Research Database; propensity scores were used to create matched groups for comparison., Setting: National Health Service neonatal units in England, Scotland and Wales., Participants: 6030 term and near-term babies, born 1/1/2010 and 31/12/2017, who received therapeutic hypothermia; 2480 babies in the matched analysis., Exposure: We compared babies that received any parenteral nutrition during therapeutic hypothermia with babies that did not., Main Outcome Measures: Primary outcome: blood culture confirmed late-onset infection; secondary outcomes: treatment for late onset infection, necrotising enterocolitis, survival, length of stay, measures of breast feeding, hypoglycaemia, central line days, time to full enteral feeds, discharge weight., Results: 1475/6030 babies (25%) received parenteral nutrition. In comparative matched analyses, the rate of culture positive late onset infection was higher in babies that received parenteral nutrition (0.3% vs 0.9%; difference 0.6; 95% CI 0.1, 1.2; p=0.03), but treatment for presumed infection was not (difference 0.8%, 95% CI -2.1 to 3.6, p=0.61). Survival was higher in babies that received parenteral nutrition (93.1% vs 90.0%; rate difference 3.1, 95% CI 1.5, 4.7; p<0.001)., Conclusions: Receipt of parenteral nutrition during therapeutic hypothermia is associated with higher late-onset infection but lower mortality. This finding may be explained by residual confounding. Research should address the risks and benefits of parenteral nutrition in this population., Competing Interests: Competing interests: CG reports grants from Medical Research Council and the National Institute for Health Research during the conduct of the study; grants from National Institute for Health Research, Mason Medical Research Foundation, Rosetrees Foundation and from Canadian Institute for Health Research outside the submitted work. He reports a grant from Chiesi Pharmaceuticals outside of the submitted work for a research study and a personal fee from Chiesi Pharmaceuticals to support attendance at an educational meeting. CG is vice-chair of the NIHR Research for Patient Benefit London Regional Assessment Panel, and has sat on the panel since 2016. CG was an unremunerated member of the Neonatal Data Analysis Unit (NDAU) steering board which oversees the National Neonatal Research Database (NNRD) until August 2020. DJ reports no potential conflicts of interest. NL reports no potential conflicts of interest. CB reports personal fees from AbbVie Pharmaceuticals outside of the submitted work; the personal fee was to support attendance at an educational meeting. CB sits on the NIHR HTA Prioritisation Panel for Maternal, Child and Mental Health Care since November 2019. KO reports no potential conflicts of interest. SO reports grants from the National Institute for Health Research, Medical Research Council, Global Challenges Research Fund, and the Arts and Humanities Research Council outside of the work on this study. JD reports grants from NIHR, the Canadian Institute for Health Research, IWK Heath Centre, Research Nova Scotia, during the study and for the study; grants from NIHR, and grants from Nutrinia, outside the submitted work. The grant from Nutrinia in 2018 was for part of his salary to work as an expert advisor on a trial. He was a member of the NIHR HTA General Board (from 2017 to 2018) and the NIHR HTA Maternity, Newborn and Child Health Panel (from 2013 to 2018)., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY. Published by BMJ.)