Objectives: To investigate the significance of neonatal thrombocytopenia and delivery method on the incidence of intraventricular hemorrhage in infants weighing <1500 g. Study Design: A total of 1283 infants weighing <1500 g who were admitted to six neonatal intensive care units over 21 months were analyzed prospectively. Illness severity was measured by the Score for Neonatal Acute Physiology (SNAP). Results: Of the infants analyzed, 145 (11.3%) had thrombocytopenia (platelet count <100 × 10⁹/L). The incidence of intraventricular hemorrhage was greater among infants with thrombocytopenia than among those without (44.8% vs 23.9%, P <.0001). Nonthrombocytopenic infants who were delivered vaginally had a higher incidence of intraventricular hemorrhage than those delivered via cesarean section (35.8% vs 15.9%, P <.0001). Thrombocytopenic infants who were delivered vaginally had the highest incidence of intraventricular hemorrhage (63.4% vs 37.5% for cesarean section, P =.005). Vaginal delivery and platelets < 50×10⁹/L on day 1 were independent risk factors for intraventricular hemorrhage (OR 2.7, 95% CI 2.0-3.8 and OR 11.2, 95% CI 3.0-42.5, respectively). Conclusions: This multicenter study confirms that thrombocytopenia and intraventricular hemorrhage are not uncommon in neonates who weigh <1500 g, and that the incidence of intraventricular hemorrhage is higher in those thrombocytopenic infants delivered vaginally. (Am J Obstet Gynecol 2002;186:109-16.)