This article provides new estimates of the number and characteristics of same-sex married couples after U.S. Supreme Court rulings in 2013 and 2015 established rights to same-sex marriage. The U.S. Department of the Treasury and the Internal Revenue Service subsequently ruled that same-sex spouses would be treated as married for federal tax purposes. Because almost all married taxpayers file joint tax returns, administrative tax records provide new information on the demographic characteristics of married same-sex couples. This study provides estimates of the population of same-sex tax filers drawn from returns filed in 2013, 2014, and 2015, using methods developed by the U.S. Census Bureau to address measurement error in gender classification. We estimate that approximately 0.48 % of all joint filers in 2015 were same-sex couples, or approximately 250,450 couples.