OBJECTIVE This study was undertaken to assess obstetric and neonatal outcomes in dichorionic twins and monochorionic-diamniotic twins after exclusion of twin-to-twin transfusion syndrome and twin reversed arterial perfusion sequence. STUDY DESIGN Data from a tertiary center were collected in twin gestations between 1994 and 2002. Chorionicity was defined by standard echographic criteria and placental examination at delivery. Neonatal outcomes were compared between monochorionic and dichorionic gestations. RESULTS This study included 503 women: 378 (75%) dichorionic and 125 (25%) monochorionic twin gestations. Monochorionic twin gestations had a higher risk of preterm deliveries between 30 and 34 weeks' gestation than pregnancies with dichorionic twins (P < .01). Monochorionic twins had a higher number of birth weight less than 10th percentile (P < .001) discordancy 25% or greater (P < .02), admission to neonatal intensive care unit (P < .03), and intraventricular hemorrhage grade 3 and 4 (P < .007) than dichorionic twins even after adjusting for gestational age. CONCLUSION Monochorionic diamniotic twins have a higher risk of perinatal complications than dichorionic twin gestations, even after exclusion of disorders unique to monochorionic placentation.