Limited data is available that estimates the effect of gestational weight gain on maternal and neonatal outcomes in term twin pregnancies in obese women. A historical cohort study of 831 obese (BMI ≥30.0 kg/m2) women in Missouri delivering 1,662 liveborn, term (≥37 weeks gestation) twin infants in 1998–2005 was conducted. Three gestational weight gain categories were examined: <25 pounds, 25–42 pounds, and >42 pounds. Adjusted odds ratios were calculated with multiple logistic regression, using the 2009 Institute of Medicine provisional guideline of 25–42 pounds as the reference group. Significant increasing trends with gestational weight gain were found for preeclampsia (p < .05), larger twin birth weight (p < .01), smaller twin birth weight (p < .001), and infants weighing >2,500 grams (p < .001). Significant increasing trends for preeclampsia and for cesarean delivery were found in concordant twin pairs (smaller twin >80% of birth weight of larger twin). Women who gained >42 pounds had a borderline significantly higher odds of preeclampsia than women who gained 25–42 pounds (adjusted OR 1.72; 95% CI 1.00–2.99, p = .052). No significant differences were found for 1-min Apgar score <4, 5-min Apgar score <7, or infant mortality ≤1 year. Our study suggests that increasing gestational weight gain is associated with larger infants but increased risk of preeclampsia and cesarean delivery in term twin pregnancies in obese women. Limiting gestational weight gain could reduce the risk of preeclampsia and cesarean delivery. Prospective studies of other study populations and maternal/infant outcomes are needed to evaluate the efficacy of the Institute of Medicine guideline.