Benzene has been encountered in a variety of occupational settings as an organic solvent and in engine exhaust originating from 1% to 5% levels in gasoline. The International Agency for Research on Cancer has classified benzene as carcinogenic to humans (Group 1) based upon increased risk of acute myeloid leukemia in occupational studies of adults. However, only a small number of studies have reported on the association of parental occupational exposure to benzene and risk of childhood and adolescent leukemias. The associations with acute lymphoblastic leukaemia (ALL) in this population-based study in Denmark. Pediatric cancer cases (<age 20) were evaluated from the Danish Cancer Registry among children born 1968-1974, and controls were selected from population records. Paternal occupation within the three months preconception and maternal pregnancy occupation were identified from nationwide pension fund records. Benzene exposure was assigned using a job-exposure matrix that had been developed for the Danish population. Risk for ALL was estimated using conditional logistic regression. Maternal occupational exposure to benzene in pregnancy was related to increased risk of ALL in offspring, while paternal preconceptional benzene exposure was not as strongly associated.