A congenitally malformed aortic valve, unicuspid (UAV), or bicuspid (BAV), occurs in about 1% of the population and is known to be more frequent in patients with aortic dissection. The clinical and operative findings in a series of 134 patients with spontaneous, acute type A aortic dissection were studied, comparing patients with normal and abnormal aortic valve morphology. The aortic valve was normal in 123 of 134 (92%) patients and abnormal in 11 of 134 (8%) patients: BAV in 10 of 134 (7.5%) and UAV in 1 of 134 (0.7%). Demographics were similar between groups, except for a lower frequency of systemic hypertension in the UAV/BAV group (46 vs 82%, p <0.01). The University of Pennsylvania malperfusion class stratification was also similar in the 2 groups. The UAV/BAV group had a greater frequency of aortic root aneurysm (64 vs 18%, p <0.01) and a larger median root diameter (5.7 vs 4.6 cm, p = 0.02). In the UAV/BAV group, the entry tear was more frequently in proximal (intrapericardial) zone 0 (91 vs 62%, p = 0.049). The frequency of abnormal aortic media histology was similar. The rate of root replacement was higher in the UAV/BAV group and early mortality was similar. The frequency of congenitally malformed aortic valve in this series was 8 times higher than in the normal population. The 1 UAV in the series was the only severely stenotic valve. In patients with type A aortic dissection with a congenitally malformed valve, aortic root aneurysm was more common and the entry tear was nearly always proximal.