The effect of delivering nutrition at different calorie levels during critical illness is uncertain, and patients typically receive less than the recommended amount.We conducted a multicenter, double-blind, randomized trial, involving adults undergoing mechanical ventilation in 46 Australian and New Zealand intensive care units (ICUs), to evaluate energy-dense (1.5 kcal per milliliter) as compared with routine (1.0 kcal per milliliter) enteral nutrition at a dose of 1 ml per kilogram of ideal body weight per hour, commencing at or within 12 hours of the initiation of nutrition support and continuing for up to 28 days while the patient was in the ICU. The primary outcome was all-cause mortality within 90 days.There were 3957 patients included in the modified intention-to-treat analysis (1971 in the 1.5-kcal group and 1986 in the 1.0-kcal group). The volume of enteral nutrition delivered during the trial was similar in the two groups; however, patients in the 1.5-kcal group received a mean (±SD) of 1863±478 kcal per day as compared with 1262±313 kcal per day in the 1.0-kcal group (mean difference, 601 kcal per day; 95% confidence interval [CI], 576 to 626). By day 90, a total of 523 of 1948 patients (26.8%) in the 1.5-kcal group and 505 of 1966 patients (25.7%) in the 1.0-kcal group had died (relative risk, 1.05; 95% CI, 0.94 to 1.16; P=0.41). The results were similar in seven predefined subgroups. Higher calorie delivery did not affect survival time, receipt of organ support, number of days alive and out of the ICU and hospital or free of organ support, or the incidence of infective complications or adverse events.In patients undergoing mechanical ventilation, the rate of survival at 90 days associated with the use of an energy-dense formulation for enteral delivery of nutrition was not higher than that with routine enteral nutrition. (Funded by National Health and Medical Research Institute of Australia and the Health Research Council of New Zealand; TARGET ClinicalTrials.gov number, NCT02306746 .).