The orthopaedic management of severe haemophilia is mainly concerned with intra-articular and intramuscular bleeding. Pseudotumour is a serious, but very rare, complication; it is a progressive cystic swelling involving muscle, produced by recurrent bleeding and accompanied by radiographic evidence of bone involvement. Ultrasonography, CT scan, MRI and vascular injection studies should be undertaken, but preoperative biopsy is contraindicated. Most pseudotumours are seen in adults and occur near the large bones of the proximal skeleton. However, a number develop distal to the wrist and ankle in younger patients before skeletal maturity. If untreated, proximal pseudotumours will destroy soft tissues, erode bone and produce vascular or neurological lesions. Surgical removal is the treatment of choice when it can be carried out in major haemophilia centres, and has a mortality rate of 20%. Regression, but not a true cure, may occur with long term replacement therapy and immobilisation; this conservative treatment is not recommended except in patients with high-titre inhibitors in whom operation is not a possibility. In these cases, percutaneous evacuation and filling with a fibrin seal or cancellous bone, depending on the size of the cavity, should be carried out. Distal pseudotumours should be treated primarily with long term factor replacement and cast immobilisation because they may respond to many modalities of conservative management. The presence of one or more progressively enlarging masses in the limbs or pelvis of a haemophiliac should raise the suspicion of a pseudotumour, although chondrosarcoma and liposarcoma have occurred in such patients.