Two studies tested the hypothesis that exposure to pornography among romantically committed individuals would increase the likelihood of intimate extradyadic behavior and that this effect would be mediated by heightened perceptions of romantic alternatives. Study 1 (n = 74) found that participants primed with sexually explicit material reported having higher quality romantic alternatives. Study 2 (n = 291) showed that initial pornography consumption predicted intimate extradyadic behavior 12 weeks later even after controlling for initial extradyadic behavior, sociosexuality, relationship length, baseline relationship satisfaction, social desirability, and participant gender and race. The relationship between pornography and intimate extradyadic behavior was mediated by perceptions of the quality of romantic alternatives. These results suggest that sexually explicit material can provoke intimate extradyadic behavior via its effect on perceptions of alternative partners.