We describe a patient with mild haemophilia B who developed symptomatic venous thromboembolism after hip arthroplasty for a traumatic fracture. A deep vein thrombosis developed in the operated leg while he was receiving a high-purity factor IX concentrate. Subsequently, he was determined to be a heterozygous carrier for the factor V Arg506Gln (Leiden) mutation. This case illustrates the importance of providing thromboprophylaxis for all patients with haemophilia receiving coagulation factor replacement and who undergo surgical procedures known to be associated with a high risk of venous thromboembolism. In patients with haemophilia and a family history of venous thromboembolism, preoperative screening for the presence of the factor V Arg506Gln mutation and other thrombophilias may be useful.