Objectives To learn the incidence and the related factors of pregnancy complicated syphilis and provide basis for policy making. Methods A cross sectional study was carried out for all pregnant women who were checked up in 29 hospitals of Shanghai and delivered between 20th, Sep. to 20 th, Dec. in 1999. Basic condition, marital and obstetric history, lab test, treatment, pregnancy outcomes and lab test on neonate were investigated. Results There were 39 cases of pregnancy complicated syphilis among 12 324 pregnant women, with an incidence of 3.16‰. All cases were in early stage. Among them, 35 cases were latent syphilis, which accounted for 89.7%; 3 cases (7.7%) were primary syphilis; 1 case (2.6%) was secondary syphilis. The average age of the patients was (27?5) years old. The related factors included: couple's education, occupation, the lab index of syphilis at premarital medical examination, the number of sexual partners of pregnant women and residential area. Only 64.1% of partuients received treatment and 48.7% of infants received serological test. Conclusions the incidence of pregnancy complicated syphilis was relatively high and most cases were latent syphilis which were widely dispersal and had adverse sequelae on fetus and neonates; The treatment and followup were not standardized. So it is in urgent need to advocate the standardized treatment and followup for pregnancy complicated syphilis. It's also important to educate among the doctors, nurses in gynecologic & obstetric department and women at their reproductive age on the knowledge about prevention and treatment on syphilis.