Thrombocytopenia is well recognized when preeclampsia is complicated by the hemolysis, elevated liver tests, low platelet count (HELLP) syndrome. We studied the effect of preeclampsia on the platelets of women whose platelet count and liver function were within normal range. We prospectively evaluated 67 preeclamptic women, gesta-tional age 30 to 42 weeks, with disease of variable severity. The platelet counts of these patients, obtained within 24 hours preceding delivery, were significantly lower than the platelet counts of 71 control subjects. The platelet counts did not differ significantly between patients with mild and severe preeclampsia. Our findings suggest the existence of subclinical thrombocytopenia in preeclamptic women whose platelet values are within normal range.