Abstract: ObjectiveTo explore influence factors of human immunodeficiency virus(HIV)and syphilis seroconversion among drug users during methadone maintenance treatment. MethodsTotally 4 909 patients from 13 community-based methadone maintenance treatment clinics in Guangdong province were followed-up for 3 years.HIV and syphilis were tested at the baseline and each year of the follow-up.Sociodemographic and drug use related information were collected using a questionnaire at baseline and every 6 months.Urine tests were also carried out by doctors every month to detect whether illegal drug was used during the treatment. ResultsThe seroconversion rate of HIV and syphilis was 0.41/100 person-years and 1.30/100 person-years.Risk factors associated with positive HIV seroconversion were marital status(relative risk RR=2.211),frequency of injection drug use(RR=1.023),sexual behaviors in previous 3 months(RR=3.614),syphilis infection status(RR=6.357),and the result of urine test at baseline(RR=3.235).High average dosage of methadone intake(RR=0.966)was a protective factor of positive HIV seroconversion.Female(RR=4.148),older age(RR=1.098),unemployment(RR=1.866),injection drug use(RR=4.515),and intercourse due to drug use(RR=17.910)in previous one month were risk factors of syphilis. ConclusionInjection drug use and sex behavior are risk factors of HIV infection and syphilis.High average dosage of methadone intake is protective factors of HIV seroconversion.