Although there are practices other than condomless anal intercourse that may result in HIV transmission among gay and bisexual men, very little is known about these 'uncommon' transmission explanations. To address this topic, the free text survey responses from 465 HIV positive gay men in Australia were thematically analysed; 123 participants offered uncommon explanations for their seroconversion. Men described several sexual acts they believed led to infection, categorised as adventurous sex (e.g., fisting) and foreplay (e.g., oral sex). Participants also identified mediating factors associated with their seroconversion, either internal (e.g., cum/pre-cum) or external (e.g., sores, illness) to sex. Finally, contextual forces associated with infection were also explored, namely physical spaces (e.g., sex on premises venues) or mental states (e.g., depression). While some uncommon explanations are unlikely to have resulted in HIV transmission, these accounts reveal the diverse and intersecting ways that men attempt to make sense of their seroconversion.