['The role of cortisol in the prediction of mortality risk in critical illness is controversial in the literature. The aim of this study was to evaluate the prognostic value of cortisol concentrations in a mixed population of critically ill patients in medical emergencies.', 'In this prospective, observational study, measurement of total (TC) and free cortisol (FC) levels was made in the serum samples of 69 critically ill patients (39 males and 30 females, median age of 74 years) at admission (0\u200ah) and 6, 24, 48, and 96\u200ah after admission.', 'Cortisol levels were determined using HPLC coupled high-resolution ESI-TOF mass spectrometry. The severity of disease was calculated by prognostic scores. Statistical analyses were performed using the SPSS 22.0 software.', 'The range of TC varied between 49.9 and 8797.8 nmol/l, FC between 0.4 and 759.9\u200anmol/l. The levels of FC at 0, 6, 24, and 48\u200ah and TC at 0, 6\u200ah were significantly elevated in non-survivors and correlated with the predicted mortality. The prognostic value of these cortisol levels was comparable with the routinely used mortality scores. In predictive models, FC at 6, 24, and 48\u200ah proved to be an independent determinant of mortality.'] Are free and total cortisol levels useful prognostic markers in critically ill patients : a prospective observational study?