Recent outbreaks of infectious syphilis across England raise concerns about the possibility of similar occurrences in London and highlight the inability of routine surveillance to detect outbreaks in a timely fashion. A rapid assessment exercise involving a cross-sectional survey of all London genitourinary medicine (GUM) clinics was therefore undertaken in April 2001, to confirm recent reports of infectious syphilis and the associated demographic and behavioural risk factors. Between 1999 and 2000, the number of diagnoses of infectious syphilis in London rose by 41% from 154 to 217. Largest rises were seen in homosexual males (38 to 67 diagnoses), and this trend persisted into the 1st quarter of 2001. Nearly half of the male homosexual cases where HIV status was known were HIV positive.