Background: Haptoglobin (Hp) polymorphism has been associated with blood pressure regulation and essential hypertension. We investigated Hp polymorphism in patients with preeclampsia. Methods: A total of 60 Caucasian women with preeclampsia were prospectively followed from hospital admission until delivery. Serum Hp phenotypes 1-1, 2-1, and 2-2 were determined by starch gel electrophoresis and compared with those in 200 normotensive controls of the same geographic and ethnic origin. Blood pressure and laboratory markers (serum uric acid, alanine aminotransferase, aspartate aminotransferase, platelet count, and 24-h proteinuria) were compared according to Hp phenotypes of preeclamptic women. Results: We found a higher Hp1 allele frequency in the preeclamptic group than in normotensive controls (0.517 vs. 0.400, p < 0.05). The Hp 1-1 phenotype was present in 28% of preeclamptic patients vs. 16% of the controls, with an odds ratio (95% CI) of 2.08 (1.05-4.08) for Hp 1-1 vs. the other Hp phenotypes. Diastolic (p < 0.005) and systolic (p < 0.05) blood pressure and proteinuria (p < 0.05) were highest in Hp 1-1 patients. Other laboratory markers were not significantly different between Hp phenotype subgroups. Conclusions: The Hp1 allele frequency was higher among preeclamptic patients and the Hp 1-1 phenotype was associated with more severe hypertension and proteinuria.