As family structures diversify, attitudes towards "nontraditional" families (e.g., same-sex-parent and cross-race families) appear to be becoming more favorable. Despite more favorable attitudes, we propose that explicitly and implicitly people view nontraditional families as less family-like than traditional (i.e., heterosexual, same-race) families. We also propose that people will hold the behavior of nontraditional (vs. traditional) families to higher standards. In Study 1, participants explicitly rated nontraditional (vs. traditional) family photos as less family-like and as less loving. In Study 2, using a reaction-time measure, participants took longer to correctly categorize nontraditional (vs. traditional) families into the family category, suggesting that at an implicit level people have greater difficulty recognizing nontraditional families as "family." In Studies 3 and 4, ambiguous (i.e., positive and negative) behavior licensed more harsh evaluations of a nontraditional family—but did not affect evaluations of a traditional family—relative to learning only positive family behavior. Despite survey data that suggest that people’s views of nontraditional families are becoming more favorable, our evidence indicates that people nonetheless harbor prejudice against certain family structures. Beyond documenting two biases against nontraditional families, this work highlights the need for prejudice researchers to examine meaningful levels of social identity, such as family units, that are intermediate between individuals and broad social classes.