We compared sociodemographic characteristics, sexual risk behaviours and sexual health experiences of 266 heterosexual black Caribbeans recruited at a London sexual health clinic between September 2005 and January 2006 with 402 heterosexual black Caribbeans interviewed for a British probability survey between May 1999 and August 2001. Male clinic attendees were more likely than men in the national survey to report: ≥10 sexual partners (lifetime; adjusted odds ratio [AOR]: 3.27, 95% confidence interval [CI]: 1.66-6.42), ≥2 partners (last year; AOR: 5.40, 95% CI: 2.64-11.0), concurrent partnerships (AOR: 3.26, 95% CI: 1.61-6.60), sex with partner(s) from the Caribbean (last 5 years; AOR: 7.97, 95% CI: 2.42-26.2) and previous sexually transmitted infection (STI) diagnosis/diagnoses (last 5 years; AOR: 16.2, 95% CI: 8.04-32.6). Similar patterns were observed for women clinic attendees, who also had increased odds of termination of pregnancy (AOR: 3.25, 95% CI: 1.87-5.66). These results highlight the substantially higher levels of several high-risk sexual behaviours among UK black Caribbeans attending a sexual health clinic compared with those in the general population. High-risk individuals are under-represented in probability samples, and it is therefore important that convenience samples of high-risk individuals are performed in conjunction with nationally representative surveys to fully understand the risk behaviours and sexual health-care needs of ethnic minority communities.