Each clinic routinely performed serology testing for syphilis on patients who might have acquired a sexually transmitted disease. Patients eligible for study included those who presented for the first time in a calendar quarter and who did not object to their blood undergoing unlinked anonymous testing for HIV. Epidemiological data were recorded and included clinic of attendance, sexual orientation, sex, whether the patient had ever injected drugs, and limited geographical characteristics which applied to lifetime HIV risk; information was collected on location of risk, nationality of sexual contact, and nationality of patient according to the categories United Kingdom, Europe, Africa, Asia, Americas, and Oceania. The process of anonymising specimens, testing them for HIV, and ascribing limited risk factor information to the results has been described previously.1 Specimens were also categorised by their geographical characteristics into three groups of increasing risk—United Kingdom, other, and Africa—specimens from people declaring any nationality or location associations with Africa being classed as Africa.