We examined whether Moral Foundations Theory helps explain Americans' reactions to violations of age-related sexual norms. Attitudes toward sexual relationships between two adolescents, an adolescent and a young adult, and two adults of highly discrepant ages were obtained from a nationally representative sample of 1,117 adults in the United States. The sex of the older person was manipulated in the age-discrepant scenarios. We found that respondents for whom purity was an important value were generally more likely to be bothered by these sexual activities. The reaction to sexual relationships between adolescent girls and young men was an exception. For this type of relationship, the negative reaction was related to the fairness foundation, suggesting that respondents thought the relationship involved exploitation. Reactions to violations of age norms were unrelated to whether respondents had a strong harm foundation, suggesting that their reactions were not motivated by concern that such relationships are harmful to participants. Finally, we found that male respondents were less likely to react negatively to age violations than female respondents, particularly when the sexual relationship involved an adolescent boy and a young woman.