BACKGROUND: The magnitude of ascending aortic degeneration in patients with bicuspid aortic valves (BAV) is controversial. METHODS: The aim of this study was to investigate ascending aortic wall degeneration in patients with BAV as compared with tricuspid aortic valves (TAV). The ascending aortic wall of 67 consecutive patients was processed for histology and immunohistochemistry. The extent of surgery and wall degeneration were investigated. Unadjusted survival was evaluated by Kaplan-Meier analysis. Median follow-up for patients with BAV and TAV was 3.8 years (interquartile range [IQR] 3.5-4.1) and 3.7 years (IQR 3.4-3.9), respectively. RESULTS: There were 33 patients with BAV and 34 with TAV. Mid-ascending aorta diameter was 54 mm (IQR 50-60). Replacement of the aortic valve, together with an ascending aortic prosthesis, was more frequent in BAV vs TAV patients (24% vs. 3%, P = 0.013). However, medial fibrosis, elastic fiber thinning, incremental medial degeneration and smooth muscle cell nuclei loss were less prominent in BAV vs TAV patients (0.1 ± 0.4 vs. 0.8 ± 1.4, P = 0.016; 0.6 ± 1.4 vs. 1.6 ± 2.0, P = 0.027; 1.7 ± 0.7 vs. 2.2 ± 0.8, P = 0.045 and 2.3 ± 1.5 vs. 3.2 ± 1.3, P = 0.026, respectively). CONCLUSIONS: Since degeneration of the ascending aortic wall was seldom prominent, histopathology alone may not support the need for surgery of the dilated ascending aorta in BAV patients as compared with TAV patients.