Epidemiologic studies of the childhood leukemias have provided information relevant to several aspects of the care and follow-up of these children. The observations made regarding in utero radiation and ALL risk have certainly curtailed the use of routine obstetric diagnostic radiographs; observations regarding the association between birth weight, fetal loss, and other gestational events provide added enthusiasm for further research into basic biologic events occurring during fetal development; and the genetic patterns of disease supply critical information for genetic counseling and follow-up of affected patients and families. Additionally, the continued epidemiologic surveillance of children with cancer serves to form the foundation from which we will assess any future changes in childhood cancer incidence or pattern. Although not discussed here, the epidemiology of late effects, including second malignancies, reproductive function, and neuropsychologic functioning will assume a more prominent role as more children survive ALL and move into adulthood. While analytic studies have yet to yield an association as strong as the lung cancer/cigarette association in adults, future research designed to isolate biologically homogeneous disease populations for study may lead us to new and important associations. The continued cooperation of large pediatric oncology groups and private physicians is crucial as these future investigations are undertaken.