Objectives: To identify incidence and predictors of Chlamydia trachomatis and Neisseria gonorrhoeae among postpartum adolescents. These estimates are compared to similar estimates among a cohort of non-pregnant, sexually active teens. Methods: 203 pregnant and 208 non-pregnant adolescents aged 14-19 years were recruited from 10 community based health clinics in Connecticut, United States. Structured interviews and sexually transmitted infection (STI) testing using ligase chain reaction (LCR) were conducted at a baseline visit (during the third trimester for the pregnant adolescents), and at 6 and 12 month follow up visits (3 and 9 months post partum, for those pregnant at baseline). Results: Among pregnant teens, new infections of C trachomatis and N gonorrhoeae increased from 7.1% at the 6 month follow up interview to 14.3% at the 12 month follow up interview; among non-pregnant teens, new infections remained relatively stable over the 6 and 12 month follow up interviews (9.0% to 8.3%) (group by time interaction, p = 0.005). C trachomatis and N gonorrhoeae prevalence was 1.9 times higher (95% CI: 0.97 to 3.89, p = 0.06) among teens in the late postpartum follow up compared to the non-pregnant teens, controlling for baseline STIs. Predictors of postpartum STIs included having a new partner and number of partners per year of sexual activity. Conclusions: Postpartum adolescents are vulnerable to STIs. Routine prenatal and postpartum care provide unique opportunities to promote condom use and other risk reduction interventions among adolescents. If sustained post partum, long term reproductive health can be promoted.