Background Perception of risk is a central construct of models of health behaviour change as it is assumed to be an intermediate step before adoption of the related safer behaviour. In the context of HIV/AIDS, the literature suggests that psychosocial factors such as stigmatising attitudes related to stereotyping people who contract HIV may infuence how people perceive their own risk of HIV infection. However, fndings on the relationships between HIV-related stigma, HIV risk perception and sexual behaviour have been inconsistent. We investigated the potential mediating role of HIV risk perception on the link between HIV-related symbolic stigma and sexual behaviour. Methods: Data used in this study are a sub-sample of 384 young adult women, aged 17–25 years, who participated in the Cape Area Panel Study conducted in Cape Town, South Africa. Study participants were asked questions relating to their demographic details, their social and economic situation, and sexual and reproductive health behaviour. The outcome measure was a composite measure of sexual behaviour derived from whether the young adult women ever had sex before, previous number of sexual partners and condom use. The mediator variable was self-perceived risk of contracting HIV. The independent variable was HIV-related symbolic stigma attitudes. Mediation analysis within the structural equation modeling (SEM) framework was used to examine if participants who held elevated stigma attitudes perceived their risk of HIV infection to be low and as a result ended up engaging in unsafe sex. Results: Higher HIV-related symbolic stigma attitudes were associated with perception of reduced risk of contracting HIV (ß=-0.248, p=0.008, 95% CI=[-0.431, -0.066]) and perception of higher risk of contracting HIV was signifcantly associated with unsafe sex practices (ß=0.179, p=0.038, 95% CI=[0.010, 0.348]). The indirect path was not signifcant (ß=-0.044, p=0.084, 95% CI=[-0.095, 0.006]), suggesting no mediation relationship. Conclusions: Stigmatising attitudes towards groups of people stereotyped as at risk of HIV infection was associated with perception of invulnerability to HIV, and the question on how this relationship afects risk sexual behaviour needs further investigation.