<i>Background:</i> There is some community survey evidence for a cohort difference in female sexual orientation. <i>Objective:</i> To determine whether there is a cohort difference in sexual orientation in Australia. <i>Methods:</i> A community survey was carried out with a sample of 7,447 adults from the age groups 20–24, 40–44 and 60–64 years. As part of this survey respondents were asked a question on sexual orientation which was answered privately. <i>Results:</i> A strong age cohort difference was found for women, with younger women more frequently reporting a homosexual or bisexual orientation. By contrast, no age cohort difference was found for men. <i>Conclusion:</i> These findings suggest that a heterosexual orientation may have become less common in younger cohorts of Australian women. This finding is consistent with data from other recent studies.