In this cross-sectional study including a heterogeneous Belgian community sample of adults (N = 1,930), two central questions were addressed pertaining to age differences of self-reported Personality Inventory for DSM-5 (PID-5) maladaptive personality traits: (a) What kind of mean-level changes occur in the PID-5 traits from age 21 to 65? and (b) What kind of variance-level changes occur in the PID-5 traits from age 21 to 65? In exploring these research questions, we also aimed to examine potential sex differences. With regard to latent mean-level age differences of the PID-5 traits, changes across adulthood were overall small to moderate and included a mix of decreasing, flat, and increasing age trends. Regarding the decreasing trends, quadratic regressions showed that the initial downward trend often either stagnated at a certain age, or subtly started increasing again from a certain age onwards. In more than half of the PID-5 traits (15/25), small but significant sex differences were found in the latent mean-level changes across adulthood. In these cases, men tended to score overall higher, except for the negative affectivity facets, on which women tended to score higher. Furthermore, variance stability was found for the majority of the PID-5 personality traits (17/25), indicating that the magnitude of individual differences in PID-5 traits is relatively stable across adulthood. Implications for individual assessment and evaluation of PID-5 scores are discussed. (PsycInfo Database Record (c) 2023 APA, all rights reserved).