Information on the prevalence and incidence of sexually transmitted infections is important for developing prevention and control strategies and allocating human and financial resources. However, there are no available estimates of such information for many areas in China. In this study, we used the existing data to make a preliminary estimation of syphilis infections in Shenzhen city, in south-eastern China. Data on prevalence rates of syphilis infections among different populations were obtained from the local HIV/sexually transmitted disease second-generation surveillance programme, and the sizes of different populations were estimated based on the most recently available figures. It was estimated that 83,760 (range 77,490-90,020) people are currently infected with syphilis, giving a prevalence of 0.71-0.82% (0.76% on average) in Shenzhen. Around 18% of these syphilis infections occur among men who have sex with men and another 15.8% and 8.7% occur among female sex workers and their clients, respectively. These estimates suggest that a combination of unprotected paid sex and sex between men may be sustaining the epidemic of syphilis in the study area. The preliminary estimates will assist the government in planning and improving its comprehensive intervention programmes for the future control and prevention of syphilis.