Group sex has consistently been identified as one of a group of risk behaviours among gay men associated with HIV seroconversion. This paper presents a detailed description of how gender, and specifically masculinity, operates as an aspect of the discourse of gay men's group sex. The findings presented in this paper are one part of a multi-aspected discourse analysis through which we are aiming to develop an account of the discourse of gay men's group sex as it was produced in a series of qualitative interviews conducted with gay men who participate in group sex. The interviews were conducted as part of the Three or More Study (TOMS), a larger project that involved a substantial quantitative component. The overarching intent of the discourse analysis is to provide as comprehensive a mapping as possible of this discursive terrain to facilitate the targeted development of HIV and sexual health educational initiatives. The discourse of gay men's group sex reproduces some key formations of masculinity within discourses of gender, which present specific challenges for HIV prevention education. These challenges are outlined at the conclusion of this paper.