Aortic stenosis is a very common disease. Current guidelines recommend intervention mainly in symptomatic patients; aortic valve replacement can be considered in asymptomatic patients under specific conditions, but the evidence supporting these indications is poor. Continuous advances in both surgical and percutaneous techniques have substantially decreased rates of perioperative complications and mortality; with this in mind, many authors suggest that earlier intervention in patients with severe aortic stenosis, when they are still asymptomatic, may be indicated. This paper summarises what is known about the natural history of severe aortic stenosis and the scientific evidence available about the optimal timing for aortic valve replacement.