['Little is known about acute changes in renal function in the postoperative period and the outcome of patients undergoing major vascular surgery. Specifically, data are scarce for patients in whom renal function temporarily decreases and returns to baseline at 3 days after surgery.', 'Retrospective cohort study.', '1,324 patients who underwent elective open abdominal aortic aneurysm surgery in a single center.', 'Renal function (creatinine clearance was measured preoperatively and on days 1, 2, and 3 after surgery. Patients were divided into 3 groups: group 1, improved or unchanged (change in creatinine clearance, +/-10% of function compared with baseline); group 2, temporary worsening (worsening > 10% at day 1 or 2, then complete recovery within 10% of baseline at day 3); and group 3, persistent worsening (>10% decrease compared with baseline).', 'All-cause mortality.', '30-day mortality rates were 1.3%, 5.0%, and 12.6% in groups 1 to 3, respectively. Adjusted for baseline characteristics and postoperative complications, 30-day mortality was the greatest in patients with persistent worsening of renal function (hazard ratio [HR], 7.3; 95% confidence interval [CI], 2.7 to 19.8), followed by those with temporary worsening (HR, 3.7; 95% CI, 1.4 to 9.9). During 6.0 +/- 3.4 years of follow-up, 348 patients (36.5%) died. Risk of late mortality was 1.7 (95% CI, 1.3 to 2.3) in the persistent-worsening group followed by those with temporary worsening (HR, 1.5; 95% CI, 1.2 to 1.4).'] Is temporary worsening of renal function after aortic surgery associated with higher long-term mortality?