Employers' health insurance coverage for legal spouses places unmarried couples at a disadvantage for obtaining coverage. Data from the Current Population Survey confirm that people with same-sex or different-sex unmarried partners are two to three times more likely to be uninsured than married people, even after controlling for factors influencing coverage. Universal partner coverage would cut that uninsured rate by as much as 50%. Employers offering domestic partner benefits would see a small enrollment increase: 0.1%-0.3% for gay and lesbian partners and 1.3%-1.8% for heterosexual partners. We find no evidence of adverse selection.