Quadricuspid aortic valve is an uncommon cause of aortic regurgitation. We report two patients who underwent aortic valve replacement because of severe aortic incompetence; the presence of a quadricuspid aortic valve was an accidental surgical finding. In one patient the aortic valve comprised two equal-sized larger cusps and two equal-sized smaller cusps, while in the other it comprised three cusps of similar size and a small accessory cusp between the right and non-coronary cusps. This report confirms the rarity of the disease and the fact that patients with quadricuspid aortic valves characterized by cusps of different sizes are more prone to develop progressive aortic incompetence because of unequal distribution of stresses on the valve. Therefore, such patients should undergo periodic, life-time echocardiographic assessment once this malformation is detected.