Prior theory and research suggest that both Cluster-B personality pathology and trait impulsivity are indirectly associated with alcohol use through positive alcohol expectancies. Yet, no prior study has investigated whether features of each of the Cluster-B personality disorders (PDs) (i.e., antisocial, borderline, histrionic, and narcissistic) and rash impulsiveness are indirectly associated with alcohol use severity through positive alcohol expectancies. In a cross-sectional design, social drinkers ( = 200; 51% female; = 26 years) completed self-report measures of trait (rash) impulsivity, Cluster-B personality disorder (PD) traits, positive alcohol expectancies, and alcohol use severity. Simple and serial mediation analyses were used to test positive alcohol expectancies and the association between trait impulsivity and alcohol expectancies as potential mediators of personality disorder trait relations with alcohol use severity. Simple mediation analyses evidenced that trait impulsivity and traits specific to each of the Cluster-B (PDs) were indirectly associated with alcohol use severity through positive alcohol expectancies. Serial mediation analyses further evidenced that the Cluster-B (PD) traits were indirectly associated with alcohol use severity via positive alcohol expectancies both uniquely from and together with trait impulsivity. Current findings are novel and suggest that positive alcohol expectancies may be important to connecting the rashly impulsive aspects of Cluster-B (PDs) with greater alcohol use severity. However, current findings also suggest that features of the Cluster-B (PDs) probably increase risk for alcohol use disorder due to other reasons (e.g., other aspects of personality or forms of impulsivity). (PsycInfo Database Record (c) 2023 APA, all rights reserved).