Purpose. This study assessed clinical manifestations and prognostic factors of critically ill patients with severe influenza admitted to the intensive care unit (ICU) in Taiwan's recent outbreak. Methodology. Patients admitted to ICU for severe influenza between January 1, 2015, and March 31, 2016, were identified and their medical records were retrospectively reviewed. The primary endpoints were outcomes and predictors of in-hospital mortality. Results. There were 125 patients with an average Acute Physiology and Chronic Health Evaluation II (APACHE II) score of 20.8. Hypertension (62.4 %) and diabetes mellitus (40.8 %) were the two most common underlying diseases. Ninety-eight (78.4 %) patients had at least one organ failure: the lungs were the most common (71.2 %), followed by the heart (53.6 %). Two of the most common symptoms of patients at ICU admission were fever (68.0 %) and cough (78.4 %). Thirty-three patients (26.4 %) died; most (40.9 %) were middle-aged (50-65 years old). A Cox regression analysis showed that multiple organ failure (MOF) [ hazard ratio (HR)=3.618; 95% CI=1.058-13.662] was significantly associated with higher risk of death. In contrast, a fluid-negative balance within 7 days of admission (HR=0.362; 95% CI=0.140-0.934) was significantly associated with a lower risk of death. Conclusion. The mortality rate of severe influenza patients admitted to the ICU was high, especially in middle-aged adults. The risk of mortality was associated with >= 2 organ failures. A negative fluid balance predicts survival.