BackgroundPeople belonging to sexual minority groups have higher levels of suicidality than heterosexuals. However, findings regarding suicide death are sparse. Using unique national data from two countries, we investigated whether individuals entering a same-sex marriage (SSM), a proxy group of sexual minority individuals, had higher suicide rates than those entering opposite-sex marriage (OSM).MethodsA cohort study of all males and females who entered an SSM (n=28 649) or OSM (n=3 918 617) in Denmark and Sweden during 1989–2016 was conducted. Incidence rate ratios (IRRs) for suicide were calculated using adjusted Poisson regression models.ResultsIn total, 97 suicides occurred among individuals who had entered an SSM compared with 6074 among those who entered an OSM, corresponding to an adjusted IRR of 2.3 (95% CI 1.9 to 2.8). For people who entered SSM, a 46% decline was noted over time from an IRR of 2.8 (95% CI 1.9 to 4.0) during 1989–2002 to 1.5 (95% CI 1.2 to 1.9) during 2003–2016. The excess suicide mortality was present in all age groups but most pronounced among younger individuals aged 18–34 years of age (IRR 2.7, 95% CI 1.5 to 4.8) and females (IRR 2.7, 95% CI 1.8 to 3.9).ConclusionThis large register-based study found higher suicide rates among individuals who entered an SSM, compared with those who entered an OSM. A lower suicide rate was noted for individuals in SSMs in recent years. More research is needed to identify the unique suicide risk and protective factors for sexual minority people.