The study objectives were to ascertain behavioural, access-related, health-seeking factors and sexually transmitted infection (STI) prevalence in young men (<25 years) attending genitourinary (GU) medicine clinics and compare them with older men (≥ 25 years) and young women (<25 years). Between October 2004 and March 2005, 4600 new attendees at seven sociodemographically and geographically contrasting GU medicine clinics across England completed questionnaires, which were linked to routine clinical data. Young men waited significantly less time to be seen in clinic compared with older men and young women. They were less likely to report symptoms than older men (P = 0.021) yet more likely to be diagnosed with chlamydia (P = 0.001) and gonorrhoea (P = 0.007). They were also more likely to be diagnosed with an acute STI relative to young women (P = 0.007). Our data confirm the need to make comprehensive STI screening readily available for young men and to develop effective and innovative screening strategies in different settings.