OBJECTIVES: To compare demographic, behavioural and HIV testing characteristics of individuals diagnosed with chlamydia infection in primary care with those in genitourinary medicine clinics, in the absence of a screening programme. The aim was to explore the current and potential contribution of primary care to the control of chlamydia. STUDY DESIGN AND METHODS: We analysed data on individuals who reported one or more chlamydia diagnoses in the past 5 years in a large probability sample survey of the resident, UK general population aged 16-44 years. Estimates were weighted and odds ratios calculated. RESULTS: Women diagnosed in primary care reported fewer sexual partners, and were less likely to have had an HIV test in the past 5 years than their counterparts diagnosed in genitourinary medicine clinics. Age, ethnicity, social class, educational attainment and urbanization of area of residence did not differ between the two groups. Too few men were diagnosed in primary care to allow for such a comparison. CONCLUSIONS: Primary care already diagnoses a large number of women with chlamydia infection, who may perceive themselves as low risk through age or sexual behaviour, yet are likely to comprise a substantial proportion of all infections. Few men are diagnosed in primary care. These groups need to be strategically targeted in the context of a future chlamydia screening programme, which will focus on the screening of younger women at high risk, and in which the role of primary care is still in development.