BACKGROUND: Critically ill patients are admitted to the pediatric ICU at all times, while staffing and other factorsmay vary by day of the week or time of day. The purpose of this study was to evaluate whether admission during off-hours is independently associated with mortality in PICUs. METHODS: A retrospective cohort study of admissions of patients <18 years of age to PICUs was performed using the Virtual PICU Systems (VPS, LLC) database. "Off-hours" was defined as nighttime (7:00 PM to 6:59 AM) or weekend (Saturday or Sunday any time). Mixed-effects multivariable regression was performed by using Pediatric Index of Mortality 2 (PIM2) to adjust for severity of illness. Primary outcome was death in the pediatric ICU. RESULTS: Data from 234 192 admissions to 99 PICUs from January 2009 to September 2012 were included. When compared with regular weekday admissions, off-hours admissions were less likely to be elective, had a higher risk for mortality by PIM2, and had a higher observed ICU mortality (off-hours 2.7% vs weekdays 2.2%; P < .001). Multivariable regression revealed that, after adjustment for other significant factors, off-hours admission was associated with lower odds of mortality (odds ratio, 0.91; 95% confi dence interval, 0.85-0.97; P = .004). Post hoc multivariable analysis revealed that admission during the morning period 6:00 AM to 10:59 AM was independently associated with death (odds ratio, 1.27; 95% confidence interval, 1.16-1.39; P < .0001). CONCLUSIONS: Off-hours admission does not independently increase odds of death in the PICU. Admission from 6:00 AM to 10:59 AM is associated with increased risk for death and warrants further investigation in the PICU population.