ABSTRACT. Background. Previous research investigating the relationship between the time of admission and mortality rates has yielded inconsistent results and has not been conducted in the pediatric intensive care unit (PICU) patient population.Objective. To determine whether an association between the time of admission (weekday versus weekend and daytime versus evening) and the risk of death exists among pediatric patients included in a cohort of children admitted to a national sample of PICUs.Design/Methods. We analyzed retrospectively a cohort of consecutive admissions to 15 PICUs included in the Pediatric Intensive Care Unit Evaluations database. The odds of death were analyzed by using mixed-effects, multivariate, logistic regression, with clustering at the hospital level. The primary independent variables were admission to the PICU on a weekend and admission to the PICU during evening hours. The severity of illness was adjusted by using the Pediatric Risk of Mortality III probability of death score.Patients. T o improve the quality of care, discrepancies in health care delivery and their effects on patient outcomes must be identified. Recent research has demonstrated that, among large patient cohorts, differences in time of admission are associated with differences in patient outcomes. Bell and Redelmeier 1 identified a significantly higher mortality rate among adult patients admitted on the weekend, compared with similar patients admitted on weekdays. Barnett et al, 2 in a study of Ͼ150 000 adult patients admitted to 38 intensive care units (ICUs), demonstrated both a higher risk-adjusted odds of in-hospital death and a longer ICU length of stay for patients admitted on the weekend, compared with patients admitted on weekdays. Similarly, neonatal mortality rates were shown to be slightly higher among infants born on weekends and during evening hours, compared with those born on weekdays and during daytime hours, respectively. [3][4][5][6][7][8] Whether an association exists between patient outcomes and time of admission in the pediatric patient population is unknown.To address this question, the Pediatric Intensive Care Unit Evaluations (PICUEs) database, representing a cohort of 34 993 pediatric ICU (PICU) patients from 15 institutions in the United States, was analyzed. 9 The objectives of this study were to compare the risk-adjusted mortality rates for weekend admissions versus weekday admissions and the risk-adjusted mortality rates for evening admissions versus daytime admissions. METHODS PatientsData for analysis were obtained from the most current available PICUEs database, Research Dataset 20 -02. 9 This database contains patient-level data from 34 993 admissions to 15 PICUs in the United States. Details of the site-selection procedures for the 15 study sites, general data-collection methods, and other analyses of this data set have been published. 9,10 Briefly, a minimum of 67 demographic, diagnostic physiologic, laboratory, and outcome data points were collected for all patients within 24 hours a...