This is a case of a 36-year-old gentleman with haemophilia A who was presented with an acute atraumatic soft tissue swelling in the right thigh. Open biopsy was performed with the resultant diagnosis of a synovial cell sarcoma. Although the clinical findings were nonspecific they could easily have been found in a bleeding haemophilic pseudotumour. The findings reported on MRI scan initially were highly consistent with those present in patients with mild haemophilia. An important part of orthopaedic management in haemophilia is concerned with intraarticular and intramuscular bleeding. Haematomas are common and sarcomas are rare. However the absence of trauma should alert the clinician to the possibility that the abnormality may represent haemorrhage into a tumour and not just haematoma, even in a haemophilic patient.