BACKGROUND: The outcomes of patients with mixed aortic valve disease (MAVD; concurrent aortic stenosis [AS] and aortic regurgitation [AR]) and its optimum management are undefined. The aim of this study was to evaluate the natural history of MAVD. METHODS: Between 2000 and 2005, 524 asymptomatic adults (mean age, 66 ± 14 years; 306 men) were identified who had mixed AS and AR, who did not undergo early intervention with surgery. The severity of AS and AR was defined using American Society of Echocardiography guideline criteria. Patients were followed over 5.5 ± 3.1 years. RESULTS: Aortic valve replacement (AVR) was performed in 349 patients (67%), and 88 (17%) died. Angina, dyspnea, or syncope developed in 292 patients (84%) before AVR; baseline left ventricular mass and the severity of AS and AR were independent predictors of progression to AVR in the overall group. Survival was associated with younger age (hazard ratio, 1.08; P < .001) and valve replacement (hazard ratio, 0.61; P = .02). Most patients with MAVD in the moderate category progressed to severe AS or AR by the time of surgery (n = 51 [27%]); symptoms were the main indication in 22 patients. In this group, AVR was associated with age, left ventricular function, valve area, and the change in peak gradient over follow-up. In patients with moderate MAVD, coronary artery disease was present in 38 (20%) at baseline and developed in 21 (21%) during follow-up but was not associated with surgery. The average time to an event (AVR or death) in patients with MAVD was 4 years. CONCLUSIONS: Careful surveillance of patients with MAVD is warranted, bearing in mind the composite severity of both AS and AR and their combined hemodynamic effects.