"One of the conjectured benefits of establishing the legal recognition of samesex partnerships is that it would promote a culture of responsibility and commitment among homosexuals. A specific implication of this claim is that "gay marriage" will reduce the prevalence of sexually transmitted infections (STI). In this study, I present a simple 2-period model, which provides a framework for discussing the ways in which gay marriage might reduce (or increase) the prevalence of STI. Then, I present reduced-form empirical evidence on whether gay marriage has actually reduced STI rates. These evaluations are based on country-level panel data from Europe, where nations began introducing national recognition of same-sex partnerships in 1989. The results suggest that these gay-marriage laws led to statistically significant reductions in syphilis rates. However, these effects were smaller and statistically imprecise with respect to gonorrhea and HIV"--National Bureau of Economic Research web site.