The association of bicuspid aortic valve with aortic stenosis, aortic regurgitation, and infective endocarditis has been known for almost 150 years and with dissection of the aorta for 75 years. 1 These complications are mentioned only briefly in cardiology textbooks3 and a standard work on medical insurance underwriting4 implies that it is usually a benign lesion: when diagnosed at routine medical examination and if the valve is functionally normal, insurance is oVered at ordinary rates. The authors also state “If there is no stenosis by age 20 years (defined as a peak gradient of less than 40 mm Hg) and only trivial insuYciency, there is an excellent chance that significant haemodynamic change will not develop before age 70.” However, on the basis of published reports by this age the majority of patients will have died or developed serious symptoms requiring surgical intervention. This review summarises the major studies that provide information on the incidence, pathology, and natural history of the bicuspid aortic valve. Clinical diagnosis of this condition was unsatisfactory before the widespread use of cross sectional echocardiography approximately 15 years ago. Most of the information in this paper therefore comes from large necropsy series and from reports on patients who have undergone aortic valve replacement. It has to be accepted that conclusions based on these reports may be inaccurate, because of nonuniformity of diagnostic criteria and varying age range, source/selection of patients studied, and study objectives.