BACKGROUND: In England, people of Black Caribbean (BC) ethnicity are disproportionately affected by sexually transmitted infections (STI). We examined whether differences in sexual healthcare behaviours contribute to these inequalities. METHODS: We purposively selected 16 sexual health clinics across England with high proportions of attendees of BC ethnicity. During May-September 2016, attendees at these clinics (of all ethnicities) completed an online survey that collected data on health service use and sexual behaviour. We individually linked these data to routinely-collected surveillance data. We then used multivariable logistic regression to compare reported behaviours among BC and White British/Irish (WBI) attendees (n = 627, n = 1411 respectively) separately for women and men, and to make comparisons by gender within these ethnic groups. RESULTS: BC women's sexual health clinic attendances were more commonly related to recent bacterial STI diagnoses, compared to WBI women's attendances (adjusted odds ratio, AOR 3.54, 95% CI 1.45-8.64, p = 0.009; no gender difference among BC attendees), while BC men were more likely than WBI men (and BC women) to report attending because of a partner's symptoms or diagnosis (AOR 1.82, 95% CI 1.14-2.90; AOR BC men compared with BC women: 4.36, 95% CI 1.42-13.34, p = 0.014). Among symptomatic attendees, BC women were less likely than WBI women to report care-seeking elsewhere before attending the sexual health clinic (AOR 0.60, 95% CI 0.38-0.97, p = 0.039). No ethnic differences, or gender differences among BC attendees, were observed in symptom duration, or reporting sex whilst symptomatic. Among those reporting previous diagnoses with or treatment for bacterial STI, no differences were observed in partner notification. CONCLUSIONS: Differences in STI diagnosis rates observed between BC and WBI ethnic groups were not explained by the few ethnic differences which we identified in sexual healthcare-seeking and use. As changes take place in service delivery, prompt clinic access must be maintained - and indeed facilitated - for those at greatest risk of STI, regardless of ethnicity.