Shackelford and colleagues (2004) found that men, compared to women, are more distressed by sexual than emotional infidelity, and this sex difference continued into older age. We conducted four high-powered replications (total N = 1,952) of this effect and found different results. A meta-analysis of original and replication studies finds the sex difference in younger samples (though with a smaller effect size), and no effect among older samples. Furthermore, we found attitude toward uncommitted sex to be a mediator (although not consistently in the same direction) between participant sex and relative distress between sexual and emotional infidelity. We hypothesize that the discrepancies between the original and replication studies may be due to changing cultural attitudes about sex across time. Confirming this speculative interpretation requires further investigation.