Surname practices in the U.S. are believed to reflect and reinforce the enduring patriarchal nature of U.S. society. Yet, some women and men reject patriarchal expectations. Calls for research accounting for such individual variations have been made. We examine the role that dispositional differences play in preferences for and reasoning about marital surnames in a sample of U.S. heterosexual women and men. With an online survey, we examined 799 heterosexual unmarried emerging adults’ (mean age = 19.9) preferences for their own and a future partner’s surname, reasons for their preferences, and associations with social cognitive dispositions relevant to self- and other-orientations: narcissism and perspective-taking. The findings suggest greater flexibility about women’s surname preferences than previously reported. Approximately one-third of men and women were open to nontraditional options. Reasons for preferences included heritage, tradition, masculinity norms, conceptions of marriage and family, identity, family pressures, and practical reasons. After controlling for age, relational status, traditionalism, autonomy, and career aspirations, lower perspective-taking was predictive of women’s preferences for both partners to retain their birth names, whereas greater narcissism was associated with women’s preferences to retain their birth name. Greater narcissism was associated with men’s desires for both partners to use his name. Taken together, the addition of individual difference dispositions provides greater insight into surname preferences and reasons for those preferences beyond gender masculinity norms.