Objective:Hypertensive diseases of pregnancy are one of the leading causes of maternal and perinatal mortality worldwide. The aim of this study was to evaluate the association between protein levels in 24-hour urine samples and maternal and perinatal outcomes in preeclamptic patients.Material and Methods:This retrospective cohort study was conducted with pregnant women who were diagnosed with preeclampsia (PE) and delivered in our clinic between 2010 and 2018. Patients were divided into those with a proteinuria value below 300 mg/24 h (non-proteinuria), proteinuria value between 300-2000 mg/24 h (mild proteinuria), proteinuria value between 2000-5000 mg/24 h (severe proteinuria) and proteinuria value >5000 mg/24 h (massive proteinuria) and were compared in terms of maternal and perinatal outcomes. Demographic characteristics (age, body mass index in kg/m2, gravidity), PE-related clinical symptoms (epigastric pain, neurological and respiratory symptoms), laboratory findings (24 h protein level, lactate dehydrogenase, aspartate aminotransferase, platelet count and creatine levels) were recorded in all patients.Results:A total of 1,379 patients meeting the study criteria were included. There were 315 (23%) patients in the non-proteinuria group, 704 (51%) in the mild proteinuria group, 234 (17%) patients in the severe group and 126 (9%) patients in the massive proteinuria group. The massive proteinuria group was found to have the highest rates of maternal and prenatal complications. The Apgar score, umbilical cord pH value, birth weight, gestational week at delivery, intrauterine growth restriction and intrauterine fetal death were significantly higher in the massive proteinuria group.Conclusion:Our data showed that the degree of proteinuria appears to be associated with maternal, fetal and neonatal outcomes among women diagnosed with PE. Women with proteinuria of >5000 mg/24 hours had notably poorer natal outcomes.