Introduction: The flu epidemic of 2012-2013 was by far the longest in the past 20 years. In the whole country, beds in intensive care units (ICUs) were occupied by patients with flu symptoms. Objective: The aim of this study was to describe the incidence of influenza-related ICU admission, demographic characteristics, clinical features and outcome of confirmed influenza A/B infection in critically ill patients admitted to our ICUs during the winter of 2012-2013. Methods: A retrospective, observational multicentre cohort study was conducted in two Dutch ICUs. A polymerase chain reaction (PCR) analysis was only done in patients with flu symptoms. All critically ill adults with confirmed influenza A or B virus infection admitted between December 2012 and April 2013 were studied. Results: During the study period 1314 patients were admitted to the ICU. A total of 111 PCR analyses were performed; 19 were positive for influenza A and 16 for influenza B. The majority of the patients were over the age of 65 and had COPD and/or a bacterial super infection. Mean ICU mortality was 28.6% as predicted by SAPS II, APACHE II and PSI score. No statistically significant differences between survivors and non-survivors were found with respect to disease severity, positive vaccination status, comorbidities and duration of ventilation. Three months after the study all remaining patients were still alive. Conclusion: During the long flu epidemic in the winter of 2012-2013 especially older patients who had COPD and/or a bacterial super infection were most affected. Mortality was not associated with positive vaccination status. © 2014, Netherlands Society of Intensive Care. All rights reserved.