We investigated the reasons for intensive care unit (ICU) readmission of patients with acute respiratory failure. Of 88 patients re-admitted to our ICU over a 15-month period, 16 were suffering from acute respiratory failure. Body weight, blood gases, time without food during the initial ICU stay and excess extracellular fluid (ΔECF) were determined. The interval until ICU readmission (D) was defined as the time between the last day of the first admission and the first day of the second admission. Significant correlations were found among the values for D, ΔECF and P/F ratio; a patient with a P/F ratio below 200 on the day of release from ICU and a ΔECF over 3 kg was likely to return to the ICU within four days. Hence, we conclude that fluid-management failure may be associated with ICU readmission in acute respiratory failure patients.