The familiar and well-established negative association between a woman's age at marriage and family size has received somewhat less attention in recent years. No doubt this is because, with the reduction in fertility of the past century, the observed differentials appear less striking and seem less significant. Age at marriage is a less obvious determinant of family size than in the past. Glass & Grebenik (1954), commenting on the data produced by the 1946 Family Census, emphasized the decreasing importance of the association both absolutely and relatively. Contrasting the completed fertility of the 1900–09 and the 1925 marriage cohorts in Great Britain (Table 1), they argued that, though for all, married women the relative influence of age at marriage was unchanged, the figures for fertile marriages only (those where the wife had at least one child) appeared to indicate ‘that age at marriage and fertility were not quite so tightly linked for the more recent group’. And they added ‘this is the kind of development which would be expected with the increasing spread of family planning’.