During anticancer treatment, oral lesions considerably aggravate the child's clinical condition and increase the risk of infection. This prospective study evaluated the incidence, nature and chronology of oral complications arising during the first 6 weeks of chemotherapy. 131 children were included in this study, and their oral and dental health evaluated on enrolment. Each child was observed once a week, for 6 weeks. Fifty-two per cent (68/131) of the children presented with at least one oral lesion. Two oral healthcare regimens (with or without tooth brushing) were evaluated. Tooth brushing significantly reduced the number of children affected. Standardised multicentre studies should permit the definition of oral care regimens which would eliminate pain and reduce the risk of infection in children hospitalised for cancer.