Patients with trisomy 21 have an increased incidence of haematological disorders, including neonatal 'leukaemoid reaction' (transient myeloproliferative disorder [TMD]), and acute leukaemias. In the past it has been felt that patients with trisomy 21 and acute leukaemia do not tolerate, and hence may not warrant, therapy as intensive as those without the syndrome. The present authors' experience and the current literature do not support this view. Two cases are reported of acute myeloid leukaemia in children with trisomy 21, successfully treated with intensive chemotherapy and bone marrow transplantation.