Preeclampsia is characterized by an imbalance in angiogenic factors, including sEng (soluble endoglin). However, the relationship of sEng with the severity of preeclampsia, clinical, and laboratory parameters, and the occurrence of adverse outcomes are not fully elucidated. We studied 1002 women with preeclampsia. Serum concentrations of sEng were measured by ELISA. Serum sEng levels were significantly different (P<0.001) in patients with preeclampsia than in healthy pregnancy. In addition, these factors were markedly different in patients with hemolysis, elevated liver enzymes, low platelet count syndrome and eclampsia than in patients with preeclampsia with or without severe features (P<0.001) and in patients with preeclampsia with severe features than in those without severe features (P<0.001). sEng correlated positively with blood pressure, proteinuria, and levels of creatinine, uric acid, aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase; and inversely with gestational age, infant’s birth weight, and platelets counts (P<0.001 for all). The risk of combined and specific adverse outcomes (pulmonary edema, acute renal failure, placental abruption, hepatic hematoma or rupture, maternal death, cerebral hemorrhage, thrombocytopenia, elevated liver enzymes, preterm delivery, small for gestational age infant, and need for endotracheal intubation, positive inotropic drug support, and hemodialysis) was higher in patients with sEng values in the highest quartile (odds ratio ≥3.1) compared with the lowest quartile. Patients in the highest quartile of sEng were more likely to deliver early compared with those in the lowest quartile (HR, 2.33; 95% CI, 1.91–2.84). We concluded that circulating concentrations of sEng seem to be a suitable marker to assess the severity of preeclampsia and are associated with increased risk of adverse outcomes.