Diffuse vascular endothelial dysfunction, secondary to oxidative stress, is an important pathological feature of preeclampsia. Oxidative conversion of low density lipoproteins (LDL) to oxidized-LDL (Ox-LDL) is considered an important step in transforming macrophages into lipid-laden foam cells destined to develop into early atherosclerotic-like lesions. In our study of 95 women with preeclampsia and 100 controls, we evaluated the association between maternal plasma Ox-LDL concentrations and preeclampsia risk. Ox-LDL concentrations were measured using a solid phase two-site enzyme immunoassay. Plasma lipids were measured using standard enzymatic procedures. We used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI) adjusted for confounders. Plasma Ox-LDL concentrations were positively correlated with cholesterol, triglyceride (TG), and LDL concentrations in cases and controls, (Spearman's r ranging from 0.39-0.48, p-values all < 0.01). There was no evidence of an increased risk of preeclampsia across increasing quartiles of Ox-LDL. The ORs for successive quartiles, with the lowest as the reference group, were as follows: 1.0, 1.1, 0.6, and 1.2. Women with extremely high concentrations of Ox-LDL (≥ 73 U/L, the upper decile), as compared with those with lower values (< 73 U/L) had a 2.7-fold increased risk of preeclampsia (95% CI 1.0-6.8). Women with high Ox-LDL and high TG concentrations (≥ 284 mg/dl), as compared with those without these two factors, had a 9.6-fold increased preeclampsia risk (95% CI 2.0-45.6). Elevated Ox-LDL, particularly in conjunction with elevated TG, appears to be a risk factor of preeclampsia. © 2005 Taylor & Francis.