Introduction Population based surveys provide valuable data for the general population but most testing for sexually transmitted infections (STI) is done in health care settings. The objective of this cross-sectional study was to describe sexual behaviour characteristics of women attending genitourinary medicine (GUM) clinics and compare them with nationally representative data.

Methods This study was conducted from January 2014 to March 2015 in two London clinics. Women were eligible if they were aged 16–29 years and able to provide informed consent. Participants completed a web-based questionnaire that included several questions from the third British National Survey of Sexual Attitudes and Lifestyles (Natsal-3). We compared clinic attenders with women aged 16–24 years in the general population, surveyed in Natsal-3 in 2010–2011.

Results We enrolled 1808 women, of whom 1806 provided clinical data and 1792 completed the questionnaire. Most (61.9%) were 16–24 years old and from white ethnic groups (48.8%). Four fifths reported having ever been tested for chlamydia with an average of 3.3 (SD 1.8) tests per participant. One third had ever been diagnosed with chlamydia. Compared with women age 16–24 years in Natsal-3, clinic attenders were more likely to report ≥5 lifetime partners (47.0% vs. 37.3%, p < 0.001) and ≥2 partners in the past year (51.8% vs. 26.7%, p < 0.001), but fewer sex acts in the past four weeks (4.1, SD 4.7 vs. 5.8, SD 6.6, p < 0.001). 43% of clinic attenders had had at least one concurrent relationship.

Conclusion This study provides detailed data about differences in sexual activity and practices between women attending clinics and those in the general population. These results can be used in studies to understand the impact of interventions such as point-of-care testing to improve chlamydia screening outcomes.

Disclosure of interest statement This study was funded by the UK Technology Strategy Board; HHL is an equity holder of the company Diagnostics for the Real World.