The purpose of this study was to establish the prevalence and clinical significance of thrombocytopenia in pregnancy-induced hypertension (PIH). Thrombocytopenia, defined as a platelet count less than 100,000/mm 3 was found in 11.6% of all patients with PIH. Logistic regression analysis was used to assess the relative contribution of thrombocytopenia, proteinuria, and the degree of hypertension to maternal and perinatal outcome. Thrombocytopenia was the principal contributor to the occurrence of abdominal pain, liver dysfunction, the presence of schistocytes in the peripheral smear, proteinuria, fetal distress, and the requirement for blood transfusions. Thrombocytopenia was also associated with a higher incidence of preterm delivery and intrauterine growth retardation. The nadir platelet count occurred within 48 hours of delivery in 56.7%(21 of 37) of cases. The median number of days for recovery of the thrombocytopenia was 2.0 days (range, 0 to 8 days). In five patients thrombocytopenia preceded the clinical manifestations of PIH. We conclude that thrombocytopenia is an independent and important risk factor for the occurrence of maternal and perinatal complications in PIH.