Two studies were conducted to explore the effects of self-stereotyping (SS) and sex role ideology (SRI) on Australian women's menstrual attitudes. In Study 1 a sample of undergraduate women at a small regional college showed significant menstrual attitude differences when grouped according to Traditional, Moderate, and Feminist SRI. In Study 2 the SRI effect was replicated in a more ethnically diverse sample of undergraduate women at a large metropolitan university. Women's own attitudes were separated from their stereotyped beliefs about most women and further analyses were conducted within the framework of social identity theory to explore the role self-stereotyping. The hypothesis that the difference between women's own menstrual attitudes and their ratings of most women's attitudes would vary as a function of degree of SS and perceived Prototype was supported. Further research is needed to clarify the SS bias.