Young people are at risk from sexually transmitted infections (STIs)—the incidence of chlamydia in the UK is highest among young women aged 16–19. Despite this, young people lack knowledge about STIs and are more aware of the risks of unwanted pregnancy than their risk of acquiring an STI. This study used qualitative and quantitative methods to examine what teenagers know about STIs, their prevention, symptoms, treatment and services. Only one-third of respondents recognized chlamydia as an STI. The little knowledge of STIs that was revealed was superficial. Few were aware that special services existed for STIs. Condoms were seen as contraception, not as a method of preventing infection transmission. High teenage pregnancy rates have received much publicity but less attention has been paid to rising STI incidence. Programmes aimed at decreasing pregnancy rates through adoption of effective hormonal contraception not only fail to address STIs but may be detrimental to prevention efforts.