Do attitudes toward and perceptions of infidelity depend on perceived relationship quality? A prediction was made that there should be a positive correlation between perceived relationship quality and negative attitudes and perceptions of infidelity, and that these correlations should be stronger for males than for females. These predictions were confirmed. More specifically, strongly negative evaluations of infidelity were reported by females regardless of relationship quality, and for males with high relationship quality. Negative attitudes toward infidelity increased for both males and females in high‐quality committed relationships, but males who reported lower relationship quality had the most favorable attitudes toward infidelity. These results are consistent with an evolutionary rationale, which suggests that males' attitudes and perceptions of infidelity depend on their perceived risk of cuckoldry.