Preeclampsia, affecting 5-8% of pregnancies, is the main cause of fetal-maternal mortality and morbidity. The differential diagnosis with chronic kidney disease (CKD) is a challenge owing to the overlapping clinical features. No biomarker has been found to discriminate between the two conditions. Here, we tested whether maternal serum levels of placental growth factor (PlGF) and soluble FMS-like tyrosine kinase-1 (sFlt-1), markers of preeclampsia, could be used to discriminate between 34 patients with preeclampsia, 23 patients with CKD during pregnancy, and 38 healthy pregnant women. Serum levels of PlGF and sFlt-1 were determined during the third trimester by commercially available immunoassays. In preeclampsia, sFlt-1 levels were significantly increased in comparison with that in CKD and in the control women. Serum levels of PlGF in preeclampsia were significantly decreased relative to both controls and patients with CKD. The sFlt-1 to PlGF ratio was significantly increased in preeclampsia (median 436) compared with controls (median 9.4) and CKD (median 4.0). No differences were found between controls and patients with CKD. Thus, our study suggests that it is possible to discriminate between preeclampsia and CKD during pregnancy by determining maternal serum levels of sFlt-1 and PlGF and their ratio.