The exchange of semen, often referred to as "cum play," has featured in gay literature and may be a unique aspect of many gay men's sexual behavior. We investigated the prevalence of "cum play" and its context among 1153 HIV-negative and 147 HIV-positive Australian gay men in an online survey. Receptive cum play (partner ejaculating or rubbing his semen over participant's anus, or participant using partner's semen as lubricant) was reported by one in six HIV-negative and one quarter of HIV-positive men on the same occasion of protected anal intercourse with a casual partner (PAIC). HIV-negative men who engaged in receptive cum play during PAIC often believed that their partner was HIV seroconcordant and tended to trust that partner. They were also generally more optimistic about the likelihood of HIV transmission, and they often only used condoms at their partners' instigation. Cum play was not uncommon and highlights the narrowness (or danger) of focusing on condom use without considering the implications of broader sexual practices and their meaning for sexual health promotion. "Safe sex" for some gay and bisexual men does not necessarily mean consistent commitment to condom use or to avoiding semen exchange. Many feel confident in their knowledge of their partner's HIV serostatus and only use condoms with these partners at their partner's request. Their commitment to safe sex may not necessarily be compromised by their practice of cum play, but the extent to which this could represent a risk for HIV transmission depends on the reliability of their assessment of their partners' HIV serostatus.