We did a retrospective study of all acute lymphoblastic leukaemia (ALL) patients on United Kingdom ALL protocol who were admitted for febrile neutropenia. The aim of the study was to document the types of infections and aetiological agents associated with febrile neutropenia and to document the factors affecting mortality. Over the 8 1/2-year period from 1986 to June 1995, there were 77 episodes in 32 children with a mean of 2.4 episodes. Morbidity due to infection was 61%; unknown causes of fever contributed 39%. Of the microbiologically documented infections, majority were Gram-negative bacteraemia. There were 7 deaths (22%) during the study period, 3 (9%) of which were due to overwhelming sepsis, with 4 contributed by the relapse status of the leukaemia. Mortality was increased by prolonged neutropenia, relapse of the leukaemia and invasive fungal infection.