The role of siblings in development has become increasingly accepted. However, the amount of research into their role in gender and gender attitude development of adults in particular remains relatively small. The purpose of this study was to explore the potential contributions of sibling relationships to the attitudes of adult men toward women and women's roles. Two hundred fifteen men completed an online survey that included the Social Roles Questionnaire (SRQ) (Baber & Tucker, 2006), the Ambivalent Sexism Inventory (ASI) (Glick & Fiske, 1996), and questions about their sibling constellations. The main hypothesis was that having a sister or sisters would be related to the endorsement of more egalitarian and less sexist views, particularly when the sister(s) were older. A statistically significant, though small, overall effect was found for the contribution of sibling constellation to scores on the ASI. In addition, men with younger sisters endorsed significantly less sexist views than men with older brothers and men with both brothers and younger sisters. Other significant findings included white men endorsing less sexist attitudes on the ASI than did non-white men, as did those with more education. There was a significant but weak correlation found between age and scores on the ASI, with younger men endorsing more sexist views than older men. White men also endorsed significantly more egalitarian/less sexist views on the SRQ. There were no other significant differences found between the groups.