Most intergenerational social mobility studies are based upon retrospective data, in which samples of individuals report socioeconomic information about their parents, an approach that provides representative data for offspring but not the parental generation. When available, prospective data on intergenerational mobility, which are based on a sample of respondents who report on their progeny, have conceptual and practical advantages. Prospective data are especially useful for studying social mobility across more than two generations and for developing joint models of social mobility and demographic processes. Because prospective data remain relatively scarce, we propose a method that corrects retrospective mobility data for the unrepresentativeness of the parental generation and thus permits them to be used for models of social mobility and demographic processes. We illustrate this method using both simulated data and data from the Panel Study of Income Dynamics. In our examples, this method removes more than 95 percent of the bias in the retrospective data.