Excess weight gain in pregnancy, as defined by the Institute of Medicine (IOM), has been linked to adverse obstetrical outcomes. However, this relationship has not been examined in the younger maternal population. Our aim was to study excess weight gain in our inner-city teenage population. In this retrospective cohort study, we reviewed all nulliparous teenage deliveries between 2000 and 2004. The groups were divided by IOM criteria into “underweight” (body mass index [BMI]<20kg/m²; n=58), “normal” (BMI, 20 to 26.0kg/m²; n=255), “overweight” (BMI, 26.1 to 29.0kg/m²; n=54), and “obese” (BMI>29.0kg/m²; n=89). The groups were then compared according to normal (control, n=257) and excess weight gain (n=199). Frequencies and odds ratios (ORs) for adverse outcomes were calculated. Excess weight gain was associated with an increased risk for cesarean delivery (OR 1.96, 95% confidence interval [CI], 1.28 to 3.01) and postpartum fever (OR, 2.46; 95% CI, 1.13 to 5.35). Significant neonatal findings included higher birthweight (3199g versus 2864g; p<0.0001) and increased risk of macrosomia (OR, 8.18; 95% CI, 2.02 to 32.99) in the excess weight gain group. We concluded that excess weight gain places teen mothers at increased risk for cesarean delivery, postpartum febrile morbidity, and macrosomia. Interventions aimed at optimal weight gain in teen pregnancies are warranted.