BackgroundMentalizing and psychological mindedness are two key, partially overlapping facets of social cognition. While mentalizing refers to the ability to reflect on one’s own mental states and the mental states of others, psychological mindedness describes the ability for self-reflection and the inclination to communicate with others about one’s own mental states.PurposeThis study examined the development of mentalizing and psychological mindedness throughout adolescence and into young adulthood, and the interplay between the two with gender and the Big Five Personality Traits.Methods432 adolescents and young adults (ages 14–30) were recruited from two independent schools and two universities. Participants completed a set of self-report measures.ResultsA curvilinear trend in both mentalizing and psychological mindedness indicated a gradual development of these capacities with age, peaking in young adulthood.Across all age groups, females had consistently higher mentalizing scores than males. For females, scores only changed significantly between age bands 17–18 to 20+ (p<0.001), ES (d = 1.07, 95% CI [.1.52–.62]). However, for males, a significant change in scores appeared between two age bands of 14 to 15–16 (p<0.003), ES (d = .45, 95% CI [.82–.07]), and 17–18 to 20+ (p<0.001), ES (d = .6, 95% CI [.1.08–.1]).The change in psychological mindedness scores differed, and females did not have consistently higher scores than males. Females’ scores were only significantly higher for ages 14 (p<0.01), ES (d = .43, 95% CI [.82–.04]), and 15–16 (p<0.01), ES (d = .5, 95% CI [.87–.11]). As with the development of mentalizing abilities, female scores in psychological mindedness remained stable from 14 to 18 years of age, with a significant change between age bands 17–18 and 20+ (p<0.01), ES (d = 1.2, 95% CI [1.7–.67]). Contrastingly, for males significant change occurred between 15–16, 17–18 (p<0.01), ES (d = .65, 95% CI [1.1–.18]) and 20+ (p<0.01), ES (d = .84, 95% CI [1.5–.2]).A significant positive association was found between mentalizing and psychological mindedness and the personality traits of Agreeableness, Openness to Experience and Conscientiousness (p<0.0001). Psychological mindedness had a weaker positive correlation with Extraversion and Openness to Experience (p<0.05).ConclusionsThe discussion is focused on the interpretation of the findings in light of social cognition and brain development research.