A short interpregnancy interval (IPI) is a risk factor for preterm delivery among women of reproductive age. As limited data exist concerning adolescents, we aimed to examine the association between short IPIs and preterm birth among adolescents using a majority of US births. Using 2007-2008 US natality data, we assessed the relationship between IPIs <3, 3-5, 6-11, and 12-17 months and moderately (32-36 weeks) and very (<32 weeks) preterm singleton live births among mothers <20 years, relative to IPIs 18-23 months. Adjusted odds ratios (aORs) and 95 % confidence intervals (95 % CIs) adjusted for maternal race, age, previous preterm deliveries, marital status, smoking and prenatal care were determined from a multivariable multinomial logistic regression model. In 2007-2008, there were 85,077 singleton live births to women aged <20 who had one previous live birth, 69 % of which followed IPIs ≤18 months. Compared with IPIs 18-23 months, short IPIs were associated with moderately preterm birth for IPIs <3 months (aOR 1.89, 95 % CI 1.70-2.10), 3-5 months (aOR 1.33, 95 % CI 1.22-1.47), and 6-12 months (aOR 1.11, 95 % CI 1.02-1.21). IPIs <3 and <6 months were also associated with very preterm birth, with aORs of 2.52 (95 % CI 1.98-3.22) and 1.68 (95 % CI 1.35-2.10) respectively. Many adolescent mothers with repeat births have short IPIs, and shorter IPIs are associated with preterm birth in a dose-dependent fashion. Increasing adolescent mothers' use of effective contraception postpartum can address both unintended adolescent births and preterm birth.