Acute leukaemia is the commonest form of malignancy in childhood. The coincidental development of leukaemia in children or adults with haemophilia is extremely rare, although cases of leukaemia and other malignancies have been reported previously in HIV-positive subjects. Of a total of 440 people with haemophilia registered with our society, two were diagnosed with acute leukaemia last year. The development of leukaemia in a subject with haemophilia has previously been reported from our country in 1985, but the negative HIV status of these recent cases is very interesting. The first caseinvolved a 14-year-old boy with moderate haemophilia A, who developed acute lymphoblastic leukaemia (ALL) [French-American-British (FAB) classification L2]. The second subject was a 16-year-old boy who had moderately severe haemophilia A with no previous family history, and developed acute nonlymphocytic (myelomonocytic) leukaemia (FAB-M4). Both patients received conventional chemotherapyand thisreport discusses the potential problems in management of such cases, including diagnosis and administration of chemotherapy in subjects with a pre-existing haemorrhagic disorder. Extensive cutaneous and mucosal bleeding, as well as bleeds in joints previously affected by haemarthrosis and alterations of haematological values were all initially suggestive of the development of inhibitors against factor VIII, but the appearance of blasts in the peripheral blood and bone marrow led to the definitive diagnosis. The risk of bleeding, due to the combination of both leukaemia and the consequences of the chemotherapy, was overcome by the administration of coagulation factor concentrates (daily initially followed by prophylactic doses after successful induction of remission in both patients). The young patient with ALL is now receiving the maintenance phase of the Children's Cancer Study Group 1961 protocol and is in the 15th month of follow-up, without any complications. The other case relapsed in the seventh month, developing enterobacter sepsis, and died. An important lesson to be learnt from these cases is that the possible diagnosis of leukaemia should not be overlooked in a patient with haemophilia and severe haemorrhagic problems, if the first-line differential diagnosis of inhibitor development against factor VIII (or IX) has been excluded.