Risk of leukemia and brain tumors among children whose parents reported occupational exposure to anticancer drugs, ionizing radiation, or anesthetics in the JECS. Cancer remains the leading cause of death by disease in children older than 1 year, and most cases have no known etiology. JECS investigators sought to determine whether exposure to anticancer drugs, ionizing radiation, or anesthetics reported by mothers during pregnancy or by fathers in the 3 months prior to becoming aware of their partner's pregnancy was associated with cancer risk in offspring up to age 3 years. Maternal exposure to anticancer drugs during pregnancy was associated with an eightfold increased risk of childhood leukemia. No associations were observed for leukemia in connection with maternal exposure to ionizing radiation or anesthetics, brain tumors in connection with any maternal exposure, or childhood cancer in connection with paternal preconception exposures. ∗Occupational exposure during pregnancy. This figure was prepared using images from Flaticon.com.