Childhood brain tumors (CBT) are the leading cause of cancer death in children; their risk factors are still largely unknown. Since most CBTs are diagnosed before five years of age, prenatal exposure and early postnatal factors may be involved in their etiology. We investigated the association between CBT and parental occupational exposure to engine exhausts in an Australian population-based case?control study. Parents of 306 cases and 950 controls completed detailed occupational histories. Odds ratios (OR) and 95 confidence intervals (CI) were estimated for both maternal and paternal exposure in key time periods. Increased risks were observed for maternal exposure to diesel exhaust any time before the child?s birth (OR 2.03, 95 CI 1.09?3.81) and paternal exposure around the time of the child?s conception (OR 1.62, 95 CI 1.12?2.34). No clear associations with other engine exhausts were found. Our results suggest that parental occupational exposure to diesel exhaust may increase the risk of CBT.