Objective: The purpose of this study was to determine the effect of corticosteroids on platelet counts and liver functions in women with pregnancies complicated by the HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome. Study Design: The study group consisted of 93 patients between 24 and 34 weeks’ gestation diagnosed with HELLP syndrome. All were given intramuscular injections of either betamethasone or dexamethasone. The 3 most common regimens used were 12 mg of intramuscular betamethasone administered twice 12 hours apart, 12 mg of intramuscular betamethasone administered twice 24 hours apart, and 6 mg of intramuscular dexamethasone administered 4 times 6 hours apart. Precorticosteroid and postcorticosteroid platelet counts and liver function test results were compared. The differences in improvement in hematologic abnormalities among the 3 corticosteroid regimens were also analyzed. Results: The hematologic abnormalities seen in the 93 patients with HELLP syndrome improved after the administration of corticosteroids. The platelet count increased by 23.3 × 10³/μL (P < .001). A statistically significant decrease was seen in liver enzyme levels. The alanine aminotransferase decreased by 31.6 IU/L, the aspartate aminotransferase decreased by 52.1 IU/L, and the alkaline phosphatase decreased by 7.6 IU/L. Of the 3 regimens used, 2 doses of 12 mg of intramuscular betamethasone given every 12 hours improved the liver function to the greatest degree. Conclusions: This study demonstrates that corticosteroids produce a significant improvement in the hematologic abnormalities associated with HELLP syndrome. Two doses of betamethasone given 12 hours apart was the most effective corticosteroid regimen. (Am J Obstet Gynecol 1999;181:304-9.)