We conducted the screening of sexually transmitted infections to define the prevalence of genital Chlamydia trachomatis and Neisseria gonorrhoeae infections and status of sexual risk behavior among homeless adolescents (10-19 yr old) in Korea. Adolescents who ran away from home and are under the care of youth shelters in ten cities in Korea served as the study population. Participants filled out a self-administered questionnaire related to sexuality. First-void urine was analyzed for chlamydial and gonococcal infection by strand displacement amplification (BDProbTec™ET, BD Diagnostic Systems, MD, U.S.A.). A total of 175 adolescents from 15 youth shelters took part in the study. Their median age was 16 yr, and 54.9% of them reported having sexual intercourse at least once. The prevalence of C. trachomatis and N. gonorrhoeae among homeless adolescents was 12.6% and 15.4%, respectively. Factors significantly associated with the infections were number of sexual partners during the past year and lifetime. This is the first community-based sexually transmitted infection (STI) screening among adolescent in Korea. Screening programs targeting sexually active adolescents are important for detection of STIs. They should be considered an alternative population-based surveillance system in order to control STIs nationally.