The British National Surveys of Sexual Attitudes and Lifestyles (Natsal) are among the largest and most detailed studies of sexual behaviour to have been undertaken anywhere in the world. Their data have been used extensively to improve understanding of sexual behaviour and to guide sexual and reproductive health policy and practice. Our group is leading on data linkage in Natsal-4 where all Natsal-4 participants will be invited to consent to link their survey and biological data to their health records and other routinely-collected data. Linking these records creates opportunities to expand the range of data we have to answer complex research questions in ways that have not previously been possible.