Variations in outcome relating to out-of-hours care have received considerable attention. We conducted a retrospective cohort study to determine the effect of day and time of admission on mortality in an intensive care unit (ICU) with representative admission severity of illness. Data pertaining to 4,183 patients admitted between 2000 and 2007 were extracted from a prospectively maintained database. Case-mix adjustment was undertaken using the UK APACHE II probability of hospital death. The mean APACHE score was 20.9 with a median predicted hospital mortality of 32.5%. Actual hospital mortality was 30.8%. Compared with Wednesdays as the reference day, admission to ICU on any other given day was not associated with higher crude or case-mix adjusted mortality. Admission to ICU in the evening, compared with daytime admission, was associated with lower odds of crude hospital mortality, but this difference was no longer significant after case-mix adjustment. Case-mix adjusted in-hospital mortality does not vary with day and time of admission, even in patients with higher severity of illness and higher predicted mortality than previously reported. © The Intensive Care Society 2013.