Previous research finds positive relationships between alexithymia and aggression. This study examined potential interpersonal factors that might elicit aggressiveness among people with high levels of alexithymia. College student participants completed the Toronto Alexithymia Scale online prior to interacting with their partners in the laboratory. Participants interacted with a partner who (i) was from their in-group versus out-group, and (ii) held similar versus different beliefs on an important topic. Results show that compared to low-alexithymic individuals, individuals with high levels of alexithymia reported increased anger after interacting with out-group members. This corresponded to increased trait aggressiveness when interacting with out-group members. No differences emerged regarding behavioral aggression. Implications for the association between alexithymia and aggression are discussed. © 2012 Elsevier Ltd.