Background: The nonspecific serine protease inhibitor aprotinin is widely used in cardiac surgery to limit bleeding. Recently, concerns about the safety of this drug were raised, especially regarding impaired renal outcome. This event rate was supposed to be dose dependent. Methods: in this observational study, the authors analyzed prospectively collected data of a single-center cardiac-anesthetic database. Adult patients treated with various dosages of aprotinin were evaluated. Logistic regression analysis identified independent predictors of renal outcome. The primary endpoint was a composite of novel postoperative renal failure requiring hemodialysis, an increased postoperative creatinine plasma concentration of 2 mg/dl or greater, or a difference between maximal postoperative and preoperative plasma creatinine of 0.7 mg/dl or greater. Results: The study analyzed 8,548 patients. Multiple logistic regression (c index = 0.861) did not show a significant association between aprotinin dosage and renal outcome, as did the bootstrap procedure (odds ratio, 0.98; confidence interval, 0.90-1.07). The most relevant predictor was a preoperatively elevated creatinine concentration (odds ratio, 11.4; confidence interval, 9.05-14.3). Patients with postoperative renal impairmerit or failure were at higher preoperative risk and/or underwent more complex procedures. In subgroups of patients with preoperatively impaired renal function (creatinine 1-5 mg/dl) (n = 1,075), complex procedures (n = 1,920), or insulin-dependent diabetes (n = 650) or patients undergoing isolated myocardial revascularization (n = 4,901), no association between aprotinin dosage and adverse renal outcome was observed. Conclusion: In the current analysis, aprotinin dosage was not associated with increased adverse renal outcome. In regard to renal outcome, this analysis did not demonstrate an essential detrimental influence of aprotinin dosage on renal function.