Objectives Circulating concentrations of the peptide kisspeptin have been proposed as a novel biomarker for early detection of pre-eclampsia. Our aims were to assess analytical and clinical performance characteristics of a commercial kisspeptin assay and to determine sensitivity and specificity of the test for pre-eclampsia. Design Prospective, longitudinal study in a United Kingdom tertiary referral Antenatal Metabolic Clinic. Patients Severely obese (body mass index, BMI > 40kg/m2, n = 194) and lean (BMI <25kg/m2, n = 78) pregnant women. Measurements A commercial kisspeptin ELISA (Phoenix Pharmaceuticals) was assessed for analytical sensitivity, specificity, precision, linearity, recovery and stability in maternal plasma samples at 16, 28 and 36 weeks gestation. Pre-eclampsia, defined using International Society for the Study of Hypertension in Pregnancy guidelines; blood pressure; delivery gestation; birthweight. Results Kisspeptin concentrations were lower in early pregnancy in obese women (P <0.001), and in women who later developed pre-eclampsia (P <0.05), compared with women with uncomplicated pregnancies. For 16-week plasma kisspeptin in prediction of pre-eclampsia, area under the receiver-operator characteristic curve was 0.80 (P <0.01), positive and negative likelihood ratios were 3.0 and 0.2, and test sensitivity and specificity were 85.7 and 71.4%, respectively. In regression analyses, kisspeptin (16 weeks) associated positively with delivery gestation (P <0.05) and birthweight (P <0.0001), and negatively with 28- and 36-week blood pressure (P <0.0001). Conclusions Kisspeptin concentration in early pregnancy is a promising biomarker for pre-eclampsia and low birthweight but cannot be recommended, in isolation, for universal screening because of inadequate test sensitivity and specificity. Large-scale studies are required to assess its potential in a panel of biomarkers.