BACKGROUND: Fever is a classic symptom in postoperative period, but to our knowledge no study shows exclusively the occurrence of fever after open aortic repair (OAR) and explores the difference between explained and unexplained fever. METHODS: Patients who underwent an OAR between March 2018 and April 2023 in Reims University Hospital were enrolled retrospectively. The primary end point was the rate of fever after OAR, which was classed in explained fever group (eFG) or unexplained fever group (uFG). Secondary outcomes were to compare fever characteristics, length of hospitalization, and mortality all causes at day 30 and day 90 between groups. RESULTS: The occurrence of fever was 23.8% after OAR, and 52% of them were unexplained. Date of occurrence of fever was at mean 3.3 days in uFG versus 7.8 days in eFG (P = 0.051). Sixty-six percent of eFG had a diagnosis of pneumopathy. The duration of hospitalization was longer in eFG versus uFG (25 vs. 15 days) and no statistical difference was found for the mortality in both groups. After at mean 806 days of follow-up in uFG, there was no occurrence of vascular graft infection. CONCLUSIONS: Fever after OAR occurred in a quarter of OAR patients and half of them were unexplained. Unexplained fever occurred earlier than eFG.