Sexual transmission of HIV from injection drug users (IDUs) to their non-IDU sex partners has been clearly documented as an important public health issue. The extent to which such 'first-wave' sexual HIV transmission will generate HIV epidemics within the wider heterosexual population is of importance for prioritisation, design and targeting of preventive interventions. In Russia, factors which will influence the scale of sexual HIV transmission outwards from IDUs include: (a) HIV prevalence and incidence among IDUs; (b) the extent and patterns of sexual mixing between IDUs and non-IDUs; (c) levels of sexual risk behaviour in these partnerships; (d) sexually transmitted infection (STI) type and prevalence in IDUs and non-IDUs. The size and behaviour of the 'bridging population', which interacts with both IDUs and the general population, as well as STI prevalence, sexual mixing patterns and sexual risk behaviour within the general population, will be crucial in determining the scale of heterosexual HIV spread. More empirical research, in conjunction with mathematical modelling of the transmission dynamics of HIV/STIs, is necessary to better understand the role of these factors in determining the nature and extent of HIV epidemics in different contexts. In Russia, there is a current need for research on bridging groups, particularly female IDU sex workers and their male clients, and for implementation of second generation surveillance, including monitoring of HIV/STI rates and risk behaviour in well-defined representative samples from both high risk groups and the general population. The many gaps in currently-available data make precise predictions of the future scale and extent of the HIV epidemic in Russia difficult. Nevertheless, existing evidence suggests that continued rapid spread of HIV among IDUs will occur, and that there is a greater risk of significant diffusion of HIV into and within the heterosexual population than has been seen as a result of IDU-associated epidemics in North America and Western Europe. Effective, high-coverage interventions aimed at simultaneously reducing injecting and sexual risk behaviour among IDUs and sex workers, as well as interventions aimed at the populations which interact with them, particularly clients of sex workers and young people, are urgently required. © 2003 Elsevier Science B.V. All rights reserved.