Objective: The aim of this study was to determine whether circulating HLA-G levels, early in pregnancy, predict the subsequent development of preeclampsia (PE). Study design: Plasma samples, collected longitudinally during the first, second, and third trimesters, from 12 PE patients and 12 matched control patients were tested for HLA-G protein using a validated sandwich ELISA. Results: First and second trimester HLA-G levels in PE were significantly lower than in control patients (first trimester, 1.25 μ g/mL vs 1.95 μ g/mL, P = .029; second trimester, 1.11 μ g/mL vs 1.90 μ g/mL, P = .024). Conclusion: Our results indicate that HLA-G levels in plasma from women who subsequently develop PE are lower than control patients, as early as the first trimester. This suggests that determination of circulating HLA-G protein concentration may be useful as an early predictor for the development of PE. Objective: The aim of this study was to determine HLA circulating, HLA-G levels, early in pregnancy, predict the subsequent development of preeclampsia (PE). Study design: Plasma samples, collected longitudinally during the first, second, and third trimesters, from 12 PE patients and 12 matched control patients were tested for HLA-G protein using a validated sandwich ELISA. Results: First and second trimester HLA-G levels in PE were significantly lower than in control patients (first trimester, 1.25 μg / mL vs 1.95 μg / mL, P = .029; second trimester, 1.11 μg / mL vs 1.90 μg / mL, P = .024). Conclusion: Our results indicate that HLA-G levels in plasma from plasma who derived develop PE are lower than control patients, as early as the first trimester. This suggests that determination of circulating HLA-G protein concentration may be useful as an early predictor for the development of PE.