Despite the contagion effect of deviant behavior in tourism settings, tourist-to-tourist effects have been largely ignored, including the joint impacts between other tourists and tourists’ companions. This study proposes that tourists who see deviant other-tourist behavior have significantly stronger deviant behavioral intentions. A questionnaire survey and four scenario-based experiments were performed to test hypothesized relationships. Findings reveal that the social contagion effect exists when tourists see deviant other-tourist behavior. Larger and more cohesive travel groups attenuate this effect, and moral disengagement mediates the social contagion effect. Theoretical and managerial implications are also discussed.