In a retrospective analysis we evaluated the occurrence of infections in 59 children with acute lymphoblastic leukemia (ALL) during the entire duration of their anticancer chemotherapy. We recorded a total of 245 infection episodes, 118 (50%) being during neutropenia and 119 (50%) during nonneutropenia. The infections most commonly detected during neutropenia were fevers of undetermined origin (36%), clinically or microbiologically defined focal infections (33%), and bacteremias (28%). During nonneutropenia, upper respiratory tract infections (55%) were the most common. Patients needed hospitalization for infections for a total of 1951 days (i.e., a mean of 33 days per patient) and the mean number of infection episodes was 4.2 per patient. Recurrent fever developed in 21% of the children with bacteremia. Mortality caused by bacteremias was 10%. Infections during the chemotherapy of ALL were a significant cause of morbidity in children, but mortality was low.