Quadricuspid aortic valve is a rare congenital malformation of the aortic valve. A case is reported of a 51 year old woman with quadricuspid aortic valve associated with regurgitation. In the past, quadricuspid aortic valve was recognised at surgery or necropsy, but now transthoracic and transesophageal echocardiography play a pivotal role in diagnosing this rare valve malformation. On occasion the transthoracic echocardiogram cannot show the quadricuspid nature of the aortic valve, and transesophageal echocardiography must be performed.