Same-sex unions are increasingly common in high-income countries that have legally recognized same-sex unions, but data from other settings are limited. In 2006, South Africa became the fifth country in the world to legally recognize same-sex unions. This study uses data from the General Household Surveys conducted in South Africa between 2002 and 2022 (483,500 men and 584,303 women aged 18 or older) to determine the proportions of cohabiting unions that are same-sex unions. On average 1.4% of men in cohabiting relationships and 1.0% of women in cohabiting relationships were in same-sex relationships. The same-sex proportion increased from 0.5% over the 2002–2006 period to 1.5% over the 2010–2018 period, before dropping in 2019 and 2022, following changes to survey procedures. The odds of men being in same-sex unions were generally highest in the most urbanized provinces, but the odds of women being in same-sex unions were less clearly associated with urbanization. Although the odds of unions being same-sex were marginally higher among Whites and Asians than among Black South Africans, the latter comprised roughly 60% of adults in same-sex unions. These results are consistent with patterns observed in high-income countries that have legalized same-sex unions, and repudiate the notion that same-sex relationships are ‘un-African’.