Among the Karo of Indonesia, the frequency of matrilateral cross-cousin (impal) marriage has declined in recent decades. We conducted a vignette experiment to assess the contributions of a handful of factors in shaping this pattern. Surprisingly, we found that cosocialization of a hypothetical woman with her impal led to increased judgments of marriage likelihood and decreased feelings of disgust in male and female respondents (n = 154). We also found that females, more than males, judged impal marriage more likely when (...) there were practical advantages. Finally, we found that younger men expressed more disgust in response to impal marriages than did older men, while women displayed an opposite but weaker reaction. This suggests the existence of gender-specific changes in attitudes toward the practice, indicating that a full understanding may require the application of sexual conflict theory. Our study illustrates the potential utility—and limitations—of vignette experiments for studying social change. (shrink)