The third edition of Making it Count [MiC III] (Hickson et al. 2003a) develops our collective approach to HIV prevention for homosexually active men by placing greater emphasis on the social contexts and structural factors contributing to HIV exposure and transmission. It argues that the health and well-being of Gay men and Bisexual men is compromised by pervasive social discrimination. It prioritises tackling homophobic and heterosexist practices at personal, institutional and structural levels and describes the roles of individuals, communities, services and policy makers in doing so. In this way, it forges a link between the HIV prevention needs of individuals, social inequality and their broader health. This paper explores the relationship between heterosexism, homophobia, social inequality and the health of homosexually active men. This section critically examines our current understandings of terms such as homophobia and heterosexism, highlighting theoretical and practical difficulties. Section 2 examines research on inequalities and discrimination within a range of settings. Section 3 considers research evidence for linking discrimination to reduced health outcomes among homosexually active men. Finally, Section 4 discusses the ways in which limitations in our understanding in this area give rise to a narrow set of health promotion interventions.