Summary. Haemorrhagic manifestations in patients with acquired haemophilia can be fatal if not recognized and treated appropriately. A retrospective analysis of the efficacy of factor eight inhibitor bypassing activity (FEIBA) in patients with acquired haemophilia treated in three medical centres in the past 10 years was conducted. The median inhibitor titre at treatment was 128 Bethesda Units (BU) in patients with severe and 34 BU in patients with moderate bleeding; P = 0.001. The majority of patients received FEIBA at a dose of 75 u kg−1 every 8–12 h. The number of FEIBA doses administered was higher in patients with severe compared with moderate haemorrhage, 10 vs. 6 doses per bleeding episode; P = 0.001. Complete response (CR) was achieved in 76% of severe and 100% of moderate bleeding episodes with a total CR of 86%. When compared with patients with human inhibitor titre <50 BU, those with titre >51 BU at treatment had lower median porcine titre, 1 vs. 9.5 BU; P < 0.05, fewer doses of FEIBA, 6 vs. 8.5 doses; P < 0.05, and shorter time to CR, 29 vs. 42 h; P < 0.05. Patients exposed to factor VIII concentrates prior to FEIBA had significantly higher maximum recorded human inhibitor titre compared with patients without such exposure, 273 vs. 38 BU; P = 0.0001. Treatment with FEIBA was very well tolerated and with very few side effects. This study provides evidence that FEIBA is an effective agent in acquired haemophilia and suitable for all types of patients regardless of severity of haemorrhage, underlying disease or inhibitor titre.