ObjectiveTo assess the repercussion of the timing of admission to the ICU upon patient prognosis. DesignA prospective, observational, non-interventional cohort study was carried out. ScopeA second level hospital with 210 operational beds and a general ICU with 8 operational beds. Patients or participantsThe study comprised all patients admitted to the ICU during 3 years (January 2010 to December 2012), excluding those subjects admitted from the operating room after scheduled surgery. The patients were divided into 2 groups according to the timing of admission (on-hours or off-hours). InterventionsNon-interventional study. Variables of interestAn analysis was made of demographic variables (age, sex), origin (emergency room, hospital ward, operating room), comorbidities and SAPS 3 as severity score upon admission, length of stay in the ICU and hospital ward, and ICU and hospital mortality. ResultsA total of 504 patients were included in the on-hours group, versus 602 in the off-hours group. Multivariate analysis showed the factors independently associated to hospital mortality to be SAPS 3 (OR 1.10; 95% CI 1.08-1.12), and off-hours admission (OR 2.00; 95% CI 1.20-3.33). In a subgroup analysis of the off-hours group, the admission of patients on weekends or non-working days compared to daily night shifts was found to be independently associated to hospital mortality (OR 2.30; 95% CI 1.23-4.30). ConclusionsAdmission to the ICU in off-hours is independently associated to patient mortality, which is also higher in patients admitted on weekends and non-working days compared to the daily night shifts.