BACKGROUND We aimed to determine the risk factors associated with mortality in patients with congenitally bicuspid aortic valve disease and dilation (<5 cm) of the ascending aorta after aortic valve replacement. METHODS We reviewed 252 patients with bicuspid aortic valve undergoing aortic valve replacement at our institution from 1971 through 2000. Patients undergoing concomitant replacement of the ascending aorta were excluded. RESULTS The average patient age was 61 +/- 15 years; 66.3% were male, and 40.5% of patients had coronary artery disease. The ascending aorta was normal (<4.0 cm) in 60.3%, mildly dilated (4.0 to 4.4 cm) in 24.2%, and moderately dilated (4.5 to 4.9 cm) in 15.5% of patients. Patients with moderate aortic dilatation had significantly lower prevalence of coronary artery disease compared with patients with normal ascending aortas (20.5% and 45.4%; p = 0.006). Mean follow-up was 8.9 +/- 6.3 years. Long-term survival was significantly different across the three groups (p = 0.004). The 5-, 10-, and 15-year estimates were 78%, 59%, and 37%, respectively, in the normal aorta group; 88%, 77%, and 46%, respectively, in the mild aortic dilation group; and 92%, 83%, and 70%, respectively, in the moderate aortic dilation group. No significant difference in cardiac death was found among the groups (p = 0.08). The significant predictors of survival using the Cox regression model were coronary artery disease, age, decade of surgery, and ejection fraction. Aortic dilation was not significant after adjusting for these other variables. At follow-up, 18 patients required reoperation, 17 for aortic valve prosthesis failure and 1 for ascending aorta aneurysm. CONCLUSIONS The present study highlights the important adverse effect of concomitant coronary artery disease, advanced age, earlier decade of surgery, and reduced left ventricular ejection fraction on survival after aortic valve replacement for bicuspid aortic valve in patients with no or mild and moderate (<5 cm) dilation of the ascending aorta.