Parenting that is high in rejection and low in acceptance is associated with higher levels of internalizing (INT) and externalizing (EXT) problems in children and adolescents. These symptoms develop and can increase in severity to negatively impact adolescents' social, academic, and emotional functioning. However, there are two major gaps in the extant literature: (a) nearly all prior research has focused on between-person differences in acceptance/rejection at the expense of examining intraindividual variability (IIV) across time in acceptance/rejection; and (b) no prior studies examine IIV in acceptance/rejection in diverse international samples. The present study utilized six waves of data with 1,199 adolescents' families living in nine countries from the Parenting Across Cultures study to test the hypotheses that (1) higher amounts of youth IIV in mother acceptance/rejection predict higher internalizing and (2) externalizing symptoms, and (3) that higher youth IIV in father acceptance/rejection predict higher internalizing, and (4) externalizing symptoms. Meta-analytic techniques indicated a significant, positive effect of IIV in child-reported mother and father acceptance/rejection on adolescent externalizing symptoms, and a significant positive effect of IIV in father acceptance/rejection on internalizing symptoms. The weighted effect for mother acceptance/rejection on internalizing symptoms was not statistically significant. Additionally, there was significant heterogeneity in all meta-analytic estimates. More variability over time in experiences of parental acceptance/rejection predicts internalizing and externalizing symptoms as children transition into adolescence, and this effect is present across multiple diverse samples. (PsycInfo Database Record (c) 2024 APA, all rights reserved).