BACKGROUND: Studies relying on outdoor pollutants measures have reported associations between air pollutants and birth weight. OBJECTIVE: Our aim was to assess the relation between maternal personal exposure to airborne benzene during pregnancy and fetal growth. METHODS: We recruited pregnant women in two French maternity hospitals in 2005-2006 as part of the EDEN mother-child cohort. A subsample of 271 nonsmoking women carried a diffusive air sampler for a week during the 27th gestational week, allowing assessment of benzene exposure. We estimated head circumference of the offspring by ultrasound measurements during the second and third trimesters of pregnancy and at birth. RESULTS: Median benzene exposure was 1.8 mu g/m(3) (5th, 95th percentiles, 0.5, 7.5 mu g/m(3)). Log-transformed benzene exposure was associated with a gestational age-adjusted decrease of 68 g in mean birth weight [95% confidence interval (CI), -135 to -1 g] and of 1.9 mm, in mean head circumference at birth (95% CI, -3.8 to 0.0 mm). It was associated with an adjusted decrease of 1.9 turn in head circumference assessed during the third trimester (95% CL -4.0 to 0.3 mm) and of 1.5 turn in head circumference assessed at the end of the second trimester of pregnancy (95% Cl, -3.1 to 0 mm). CONCLUSIONS: Our prospective study among pregnant women is one of the first to rely on personal monitoring of exposure; a limitation is that exposure was assessed during 1 week only. Maternal benzene exposure was associated with decreases in birth weight and head circumference during pregnancy and at birth. This association could be attributable to benzene and a mixture of associated traffic-related air pollutants.