There is considerable variability in bleeding patterns of severe haemophilia (<1% factorVIII). Knowledge of the contribution of thrombophilic factors in these patterns may improve individually tailored treatment strategies. We reviewed the literature regarding the relation between prothrombotic factors and clinical phenotype of severe haemophilia. Medline and EMBASE were searched for relevant articles. 9369 articles published between 1963 and September 2003 were screened and seven relevant papers were retrieved. Each of these reported on a different combination of thrombophilic factors. Presence of the factor V Leiden mutation appears to decrease the severity of severe haemophilia most consistently. Findings on other thrombophilic factors were inconclusive. There is a clear need for additional research on potential determinants of phenotypes of severe haemophilia before such knowledge can be translated into individual care for severe haemophilia patients with confidence.