ABSTRACT Based on longitudinal data from the Institute of Human Development Intergenerational Study, the use and change in defense mechanisms of more than 150 individuals, as assessed from TAT stories, was studied across ages 11, 12, and 18. The findings of this study, based on an earlier generation, were generally consistent with cross-sectional findings from current samples, showing that the defenses of projection and identification were used more frequently than denial at all three ages and that the use of projection and identification increased from early to late adolescence. However, unlike current findings, the 18-year-olds did not show greater use of identification than of projection, perhaps due to IQ differences between this community sample and the samples of more recent studies.