BackgroundWe propose and evaluate a contribution to the conceptualization and assessment of personality functioning based on social domains and mentalizing hypotheses. Social domains are distinct social contexts, such as with acquaintances and friends, with differentiated expectations regarding participants' behaviours and social attributions. The capacity to organize social participation according to these expectations requires the ability, we suggest, to modulate mentalizing processes domain by domain. Drawing on evidence that social domain organization is impaired in borderline personality disorder (BPD) and that hypermentalizing, a heightened interpretation of others' motives, thoughts or emotions, is elevated in adolescent BPD, we hypothesized that hypermentalizing levels in adolescents will vary by social domain and that elevated BPD features will be associated with impairment of this domain organization of hypermentalizing.MethodsMeasures including the borderline personality features scale for children (BPFSC) and the movie for the assessment of social cognition (MASC) were administered to 171 adolescents aged 12–17 recruited from public schools and community organizations in a large metropolitan area in southwestern United States. Mean hypermentalizing scores were computed for adolescent interpretations of sequences in the MASC focusing on the social domains of acquaintance, friends and romantic interactions.ResultsThere was a progressive increase in hypermentalizing scores across the acquaintance, friends and romantic interactions (repeated measures ANOVA, p < .001, all pairwise comparisons, p ≤ .02), which was markedly reduced in the presence of elevated BPD features (interaction term, p = .007).ConclusionsHypermentalizing is organized according to social domain and this organization is impaired in the presence of elevated BPD features. The findings are consistent with the proposal that personality functioning entails a social domains organization of hypermentalizing, which is impaired in personality dysfunction. Identifying mentalizing processes domain by domain has the potential to create a personalized focus for the treatment of adolescents with personality difficulties.