Ecstasy has become one of the most widely used illicit drugs in Australia. This study investigated outcome expectancies as possible motivating and maintaining factors in ecstasy use and sexual risk-taking behaviour. A sample of regular ecstasy users (N = 220) from Sydney and Canberra, Australia, was recruited for structured face-to-face interviews. They also completed an Ecstasy Expectancy Questionnaire. Seven of eight subscales significantly differentiated regular users from non-users. Interestingly, light and heavier users held similar outcome expectancies, except that light users endorsed items on the sexual enhancement subscale more strongly than heavier users. Further investigation showed that the level of sexual risk taking observed in this sample was high, with the majority of participants reporting multiple partners, “casual” sexual encounters, sex under the influence of substances, and inconsistent condom use. Using logistic regression analyses, a key finding was that positive sex-related ecstasy outcome expectancies were associated with involvement in disinhibited sexual behaviour under the influence of ecstasy. These effects persisted after statistically controlling for the frequency of ecstasy use. The findings suggest that sexual risk taking is related not only to the disinhibiting properties of ecstasy but also to beliefs that users hold about the effects of the drug.