The aim of this article is to analyse the effect of social mobility on fertility behaviour. A theoretical model is discussed that combines Easterlin's theory on the relationship between resources and aspirations, with a key assumption of the interpretations of the persistence of inequality in educational and social mobility opportunities put forward by Boudon and Goldthorpe. The hypothesis drawn from this explicative model is that, everything else being similar, individuals will decide to become fathers when they manage to achieve a similar socioeconomic position to that of their family of origin. This hypothesis was tested with data drawn from the first wave of Ilfi (Italian Longitudinal Household Survey). The transition to first children among Italian men born in the last century is studied by means of event history analysis models. The results of the empirical analysis confirm that difficulties in achieving an adequate socioeconomic position are among the factors that contribute to the delay in fatherhood.