One conjectured benefit of a marriage-like legal status for same-sex couples is a reduction in the incidence of sexually transmitted infections (STI). In this study, I discuss how such a policy might influence risky sexual behaviour and STI rates. I also present reduced-form empirical evidence on whether same-sex partnership laws have reduced STI rates, using country-level panel data from Europe. The results suggest that these laws led to statistically significant reductions in syphilis but not in infections that are not sexually transmitted. However, their effects on the incidence of gonorrhoea and HIV were also smaller and statistically imprecise.