This paper describes the prevalence of, and risk factors for, exposure to syphilis in a random sample of male and female prisoners. We found that only 2% of male and 1% of female prison inmates in New South Wales (NSW) had confirmed evidence of untreated syphilis, and none appeared to be in an infectious phase. In the multivariate analysis, indigenous ethnicity remained the most potent predictor for confirmed syphilis (either past or present). There was some evidence to suggest that syphilis among indigenous prisoners may be associated with limited access to health services outside prison. The epidemiology of syphilis reflects that of the general community suggesting that prisons could be used as sentinel sites to help evaluate the effectiveness of STD prevention and control strategies.