Between 1988 and 1995, 341 children with acute myeloid leukaemia (AML) were treated on the Medical Research Council Acute Myeloid Leukaemia Trial (MRC AML10). The 5-year overall survival was 57%, much improved on previous trials. However, there were 47 deaths (13. 8%), 11 of which were associated with bone marrow transplantation (BMT). The treatment-related mortality was significant at 13.8%, but decreased in the latter half of the trial from 17.8% in 1998-91 to 9. 6% in 1992-95 (P = 0.03%). The main causes of death were infection (65.9%), haemorrhage (19.1%) and cardiac failure (19.1%). Fungal infection was a significant problem, causing 23% of all infective deaths. Haemorrhage occurred early in treatment, in children with initial white cell counts >100 x 109/l (P = 0.001), and was more common in those with M4 and M5 morphology. Cardiac failure only occurred from the third course of chemotherapy onwards, with 78% (7/9) in conjunction with sepsis as a terminal event. Some deaths could be prevented by identifying those most at risk, and with prompt recognition and aggressive management of complications of treatment. Future options include the prophylactic use of antifungal agents, and the use of cardioprotectants or alternatives to conventional anthracyclines to decrease cardiac toxicity.