Persistent high-titre inhibitors after immune tolerance induction (ITI) increase the risks of haemorrhage and arthropathy, resulting in high morbidity and mortality. Long-term prophylaxis with bypassing agents may avert these risks. This study was performed to assess the effectiveness and safety of early prophylaxis with FEIBA in preventing bleeding and joint damage after failed ITI. Seven paediatric patients proceeded immediately after failed ITI to long-term FEIBA prophylaxis at 60-100 IU kg(-1) dosages and various dosing intervals depending upon bleeding tendency. Bleeding episodes and joint status were assessed. Thrombin generation assays (TGA) were also used to gauge treatment response. FEIBA prophylaxis was commenced at a median age of 6.0 years (range, 1.5-11.8 years) and continued for a median duration of 6.9 years (range, 0.8-17.1 years). The mean annual incidence of joint bleeding was 1.5 episodes per year with a 95% CI of 0.7-3.0 episodes per year. Muscle bleeding incidence was 0.9 episodes per year (CI, 0.6-1.2 episodes per year). No patient experienced major joint damage during prophylaxis. Median Pettersson and orthopaedic joint scores at the last follow-up evaluation were 4 (range, 0-12) and 2 (range, 0-4) respectively. Endogenous thrombin potential (ETP) measured by TGA exceeded 80% of normal after FEIBA infusion in the majority of the patients. Between regular prophylactic infusions, mean trough ETP equalled 2.6 fold of the inhibitor plasma control mean. FEIBA prophylaxis was well-tolerated without serious thrombotic or other complications. The only adverse event involved venous access. Therefore early long-term FEIBA prophylaxis is valuable in controlling bleeding and preserving joint integrity in young patients failing ITI.