In the debate about whether or not narcissism has been increasing in recent history, there is a lack of basic information about how narcissism changes across the adult life span. Existing research relies on cross-sectional samples, purposely restricts samples to include only college students, or follows one group of individuals over a short period of time. In the current study, we addressed many of these limitations by examining how narcissism changed longitudinally in a sample of 747 participants (72.3% female) from Age 13 to Age 77 across 6 samples of participants born between 1923 and 1969. Narcissism was moderately stable across the life span (rs ranged from .37 to .52), to a comparable degree as other psychological characteristics. We found that more maladaptive forms of narcissism (e.g., hypersensitivity, willfulness) declined across life and individual autonomy increased across life. More later-born birth cohorts were lower in hypersensitivity and higher in autonomy compared with earlier-born birth cohorts; these differences were most apparent among those born after the 1930s. The results are discussed in the context of the mechanisms that drive both changes in narcissism across the life span and substantive differences in narcissism between historical periods. (PsycINFO Database Record (c) 2019 APA, all rights reserved).