We examined how the amplification of 3 within-person processes (behavioral reactivity to interpersonal perceptions, affect reactivity to interpersonal perceptions, and behavioral reactivity to a person's own affect) accounts for greater quarrelsome behavior among individuals with borderline personality disorder (BPD). Using an event-contingent recording (ECR) methodology, individuals with BPD (N = 38) and community controls (N = 31) reported on their negative affect, quarrelsome behavior, and perceptions of the interaction partner's agreeable-quarrelsome behavior in interpersonal events during a 20-day period. Behavioral reactivity to negative affect was similar in both groups. However, behavioral reactivity and affect reactivity to interpersonal perceptions were elevated in individuals with BPD relative to community controls; specifically, individuals with BPD reported more quarrelsome behavior and more negative affect during interactions in which they perceived others as more cold-quarrelsome. Greater negative affect reactivity to perceptions of other's cold-quarrelsome behavior partly accounted for the increased quarrelsome behavior reported by individuals with BPD during these interactions. This pattern of results suggests a cycle in which the perception of cold-quarrelsome behavior in others triggers elevated negative affect and quarrelsome behavior in individuals with BPD, which subsequently led to more quarrelsome behavior from their interaction partners, which leads to perceptions of others as cold-quarrelsomeness, which begins the cycle anew.