All-Cause and External-Cause Mortality Disparities Among Australians in Same-Sex Relationships Before and After Marriage Equality: A Nationwide Cohort Study, 2011-2023.

Abstract

<b>Objectives.</b> To examine secular trends in mortality among Australians in same-sex and different-sex relationships. <b>Methods.</b> Using Australian Census-linked mortality records (2011-2023), I used Cox proportional hazard models to estimate all-cause and external-cause mortality risk among adults in same-sex relationships (n = 54 529) and different-sex relationships (n = 7 923 328), separately by sex. Inverse probability weights balanced comparators on age, educational attainment, and household income. I stratified results into periods before and after Australia's 2017 legalization of same-sex marriage. <b>Results.</b> Compared with those in different-sex relationships, women and men in same-sex relationships experienced elevated all-cause mortality risk (hazard ratio [HR] = 1.25; 95% confidence interval [CI] = 1.15, 1.35 and HR = 1.24; 95% CI = 1.16, 1.31, respectively) and external-cause mortality risk (HR = 2.56; 95% CI = 2.01, 3.26 and HR = 1.96; 95% CI = 1.64, 2.71, respectively). Inequalities in external-cause mortality risk were significantly elevated in both periods before and following marriage equality. (HR = 3.40 and 2.04 in the pre- and postreform periods, respectively, among women in same-sex relationships, and HR = 2.01 and 1.93, respectively, among men in same-sex relationships). <b>Conclusions.</b> Australians in same-sex relationships experienced elevated mortality risk relative to those in different-sex relationships, with inequalities persisting after marriage equality. Routine collection of sexual orientation in the Australian Census would support ongoing monitoring of these disparities. (<i>Am J Public Health</i>. Published online ahead of print September 17, 2026:e1-e9. https://doi.org/10.2105/AJPH.2026.308712).