OBJECTIVE To investigate whether serum N-terminal pro-brain natriuretic peptide (NT-proBNP) levels could be used as a marker to determine the severity of preeclampsia. METHODS This prospective cohort study included pregnant women with preeclampsia and severe preeclampsia and normotensive pregnant controls admitted between January 2013 and July 2014. Preeclampsia was graded according to the recently revised criteria of the American College of Obstetricians and Gynecologists (ACOG). Serum NT-proBNP levels were compared among the groups. RESULTS Of the 49 women with preeclampsia, 25 had severe preeclampsia. The controls were 27 normotensive pregnant women admitted during the same period. Serum NT-proBNP levels were significantly higher in the preeclampsia groups than in the control group (p < 0.001). In addition, NT-proBNP levels were significantly higher in the severe preeclampsia group compared with both the preeclampsia group (p < 0.001) and the control group (p < 0.001). CONCLUSION The ACOG has recently revised the grading of hypertensive diseases of pregnancy and the criteria for severe preeclampsia. In line with these revised guidelines, serum NT-proBNP levels appear to be a useful marker to evaluate the severity of preeclampsia.