OBJECTIVE: The purpose of this study was to determine the incidence of neurologic morbidity in preterm monochorionic (MC) and dichorionic (DC) twins. STUDY DESIGN: We collected perinatal, neonatal, and infant follow-up data of 76 MC and 78 DC twins born between 24 and 34 weeks of gestation (295 infants). Risks of neuromorbidity in the surviving infants were evaluated in relation to chorionicity, discordant birth weight (>20%), twin-twin transfusion syndrome (TTTS), and cotwin death. RESULTS: The overall incidence of cerebral palsy and minor neurologic disabilities in surviving twins was 4% and 9%, respectively. MC infants had a higher incidence of cerebral palsy (8% vs 1%, P<.05) and neurologic morbidity (15% vs 3%, P<.05) than DC infants. The risk of impaired neurodevelopment was higher in MC infants with discordant birth weight (42%, P<.01), TTTS (37%, P<.01), and cotwin death (60%, P<.01) than those with concordant birth weight (8%). In MC pregnancies, the cerebral palsy risk was higher in infants with discordant birth weight than those with chronic TTTS (19% vs 4%, P<.05). Similarly, discordant DC infants had higher neuromorbidity than concordant group (5% vs 1%, P