We report an increased incidence of infectious deaths during maintenance treatment of the ninth protocol for acute lymphoblastic leukaemia of the Dutch Childhood Oncology Group (DCOG-ALL-9). The main difference in maintenance treatment between DCOG-ALL-9 and the DCOG-ALL-7 and DCOG-ALL-8 protocols is the interruption of methotrexate and 6-mercaptopurine by vincristine (2mg/m(2) weekly) and dexamethasone (6mg/m(2) daily) for 14 days every 7 weeks in the DCOG-ALL-9 protocol. The 1107 children treated with the DCOG-ALL-7, DCOG-ALL-8 or DCOG-ALL-9 protocol were included and screened for infectious death during maintenance treatment (July 1988-July 2002). Seven of the 510 children died of severe infections during the maintenance phase of DCOG-ALL-9, compared to none of the 597 patients during the DCOG-ALL-7 and DCOG-ALL-8 protocols (1.37% versus 0.0%; p=0.013). Results from the current study suggest that repeated, prolonged exposure to dexamethasone results in an increase of lethal infections from 0% to 1.37%. In the dosing-schedule used, the advantage of dexamethasone may not outweigh the higher risk of infectious death.