Despite poorer health and healthcare outcomes experienced by lesbian, gay and bisexual adults, data for research to characterize and address these disparities remain limited. We describe sexual history information from 502,543 UK Biobank participants recruited between 2006 and 2010, as sexual identity was not collected from the cohort at baseline, and compare this with sexual history and sexual identity responses to the third National Survey of Sexual Attitudes and Lifestyles (NATSAL-3), collected between 2010 and 2012. After exclusions, 700 (0.3%) women and 2112 (1.2%) men in UK Biobank reported a history of exclusively same-sex sex and 5162 (2.3%) women and 4275 (2.3%) men reported a history of sex with both women and men; estimates were consistent with, although slightly lower those from NATSAL-3. UK Biobank is an important resource for sexual minority health research.