This analysis assesses change between 1940 and 1980 in the proportion of young adults (age 18-25) who live with their parents, based on a comparison of contemporaneous data drawn from the United States censuses of 1940, 1960, and 1980 and retrospective data reported by respondents in the National Survey of Families and Households of 1987-88. The authors also compare reports on marital status from both sources. The goal is to assess the validity of retrospective data on leaving home. The authors use graphs by single years of age of (1) the proportions living in the childhood home, and of (2) the proportions married based on each source. The timing of the marriage transition is recalled very similarly to contemporaneous reports in the censuses. However, this is not the case for living arrangements. Respondents report a substantially earlier age at leaving home than is consistent with living arrangements reported in these three censuses, even when those who reported returning home at any time in the two years surrounding the census dates are recoded as living at home.