Low birthweight individuals not only have increased risk of cardiovascular disease themselves, but cardiovascular disease risk is also increased in their parents. The mechanisms underlying these trans-generational associations are not fully understood. We hypothesise that, in part, they reflect the trans-generational effects of poor maternal environmental circumstances in early childhood. Adverse environmental factors acting early in the mother's life will not only influence her own predisposition to cardiovascular disease but will also result in adverse consequences – low birthweight and increased cardiovascular disease risk in later life – for her offspring. Adult leg length is a valid indicator of early life environmental circumstances, in particular of infant nutrition. If our hypothesis is correct, then adult leg length should be positively associated with offspring birthweight. In this study of 4286 randomly selected women aged 60–79 years from 23 towns across England, Scotland and Wales, the magnitude of the association between leg length and offspring birthweight was greater than the association between trunk length and offspring birthweight. After control for potential confounding factors, offspring birthweight increased by 89.8 g [95% confidence interval 66.1, 113.5 g] for each standard deviation increase in maternal leg length, and by 55.2 g [32.2, 78.1 g] for each standard deviation increase in maternal trunk length. The association between leg length and offspring birthweight was unaffected by adjustment for maternal birthweight, but the association between trunk length and offspring birthweight was attenuated to 38.0 g [1.0, 74.9 g]. These findings support the hypothesis that adverse early childhood environmental circumstances affect not only the vitality and health of the woman in later life but also the birthweight of her offspring, and suggest that the trans-generational association between birthweight and cardiovascular disease is in part explained by early childhood maternal environmental circumstances.