This research examines how the cultural dimension of uncertainty avoidance—a person’s (in)tolerance for uncertain or unknown situations—impacts communication alignment in crisis negotiations. We hypothesized that perpetrators high on uncertainty avoidance would respond better to negotiators who use formal language and legitimize their position with reference to law, procedures, and moral codes. Data were transcriptions of 53 negotiations from a Dutch–German police training initiative, where police negotiators interacted with a high (German) and low (Dutch) uncertainty-avoidant mock perpetrator. Consistent with accounts of cross-cultural interaction, negotiators tended to achieve more alignment in within-culture interactions compared to cross-cultural interactions. Moreover, German negotiators, who scored higher on uncertainty avoidance than the Dutch negotiators, were found to use more legitimizing messages and more formal language than their Dutch counterparts. Critically, irrespective of the negotiators cultural background, the use of these behaviors was a significant moderator of the degree to which negotiator and perpetrator aligned their communicative frames: Using legitimizing and formal language helped with German perpetrators but had no effect on Dutch perpetrators. Our findings show the effects of cultural background on communication alignment and demonstrate the benefits of using more formal language and messages that emphasize law and regulations when interacting with perpetrators high on uncertainty avoidance.