Although the basic management of people with haemophilia is agreed, much of this is based on historical experience. By today's standards the precise details of how much treatment is enough are not based on a good evidence framework. Although regular treatment with prophylaxis is widely believed to be optimal, the evidence for this has not been considered strong enough by some authorities to justify the considerably increased expenditure. Reviews available on the Cochrane Database provide regularly updated evidence in a given field and, where there is inadequate evidence, a review may identify what kinds of trials are needed. The Cochrane Review Group have identified 152 references to 127 trials relating to haemophilia A and B, and von Willebrand disease. Most of the trials in haemophilia are short-term comparisons of treatments such as trials with coagulation factor concentrates, or studies of antiviral agents. One study of bleeding prophylaxis ('Clotting factor concentrates given to prevent bleeding and bleeding-related complications in people with haemophilia A and B') has been designed but is not yet completed, and another title ('Management of inhibitors with haemophilia A') has been registered. Some preliminary questions can establish areas where new clinical studies are needed.