Introduction There is an established causal relationship between benzene exposure and acute myelogenous leukaemia in adults, but the association between parental benzene exposure and childhood leukaemia in offspring remains inconclusive.

Objective Using the prospective population-based Norwegian Mother and Child Cohort Study (MoBa) comprising 1 13 754 offspring (1999–2009), we investigated the association between parental exposure to ”gasoline or exhaust” as a proxy to benzene exposure and childhood leukaemia.

Method Around the 17th gestational week mothers and fathers responded to questions on a range of occupational exposures during the last 6 months and pre-conception, respectively. Exposure to benzene was assessed through self-reported exposure to ”gasoline or exhaust” (”never exposed”, ”ever exposed” and ”exposed>30 days”), the latter interpreted as being occupational. Development of subsequent childhood leukaemia (n=70) were identified through linkage with the Cancer Registry of Norway. The risk was estimated by odds ratios (OR) with 95% confidence intervals (95% CI) comparing the offspring from exposed and unexposed parents using a logistic regression model, adjusting for maternal smoking and birth weight.

Results Maternal exposure was associated with an increased risk of childhood leukaemia (OR 2.6; 95% CI 1.03, 6.50). The risk increased with number of days being exposed during the last 6 months categorised in ”0”, ”1–30”, ”31–180” (p-value for trend=0.03). No excess risk of leukaemia was found for paternal exposure.

Conclusion We found an excess risk of leukaemia in children having a mother reporting being exposed to benzene-containing ”gasoline or exhaust” prior to and/or during pregnancy.