Low birthweight is often used as a health indicator. This paper reports the findings of a cohort study, which were analysed to determine the relationship, if any, between the age of the mother and birthweight given the mother's smoking habits and the level of social deprivation of the mother's place of residence. The data used were extracted from those data routinely collected by the Information and Statistics Division of the National Health Service, Scotland. Information on 178,801 singleton live births occurring between 1992 and 1994 was used in the analysis. The factors considered were those available directly from the official records. The level of social deprivation was measured using Carstairs index based on the postcode sector. Although younger and older mothers have lighter babies, on average, it was found that this effect can be largely explained by differences in the smoking habits and level of deprivation of the mothers. Birthweight, adjusted for gestational age, sex of the baby and parity of the mother, was significantly lower for babies born to mothers who smoked during pregnancy. It is clear, however, that the detrimental effect of smoking increases with the age of the mother. Although adjusted birthweight was lower for those in areas of high deprivation, this effect is small compared with the effect of smoking. Any attempt to decrease the percentage of low-birthweight babies must focus on reducing the percentage of mothers who smoke.