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The objective of this study was to examine the association between maternal smoking during pregnancy and offspring height and its components. The analysis was based on 6,340 white singletons born in 1991-1992 and enrolled in the Avon Longitudinal Study of Parents and Children (ALSPAC), who had maternal smoking data recorded for at least one trimester in pregnancy, and who had their height recorded at age 7.5. Smoking at any time in pregnancy was associated with a reduction in offspring height, trunk, and leg length, and the leg-to-trunk ratio, after adjustment for age and sex. After additional adjustment for maternal factors, social factors, and breastfeeding, associations with leg length and leg-to-trunk ratio remained, with reductions of 0.25 cm (95% confidence interval, 0.05-0.46 cm) in leg length and 0.30% (95% confidence interval, 0.03-0.57%) in leg-to-trunk ratio if the mother smoked. Findings were similar when the smoking data were analyzed separately for each trimester. Furthermore, in each trimester, the more a mother smoked, the greater the reduction in offspring height, leg length, and leg-to-trunk ratio. These dose-response relationships remained after adjustment for all potential confounders for leg length and leg-to-trunk ratio. Smoking at any time in pregnancy reduces offspring height and its components, and in particular leg length and leg-to-trunk ratio at age 7.5.