Objectives To estimate the change in the diagnostic prevalence of preeclampsia after introduction of revised definitions of preeclampsia in the 2013 ACOG Report of the Task Force on Hypertension in Pregnancy. Methods A multicenter, prospective, observational study was conducted in 24 maternity units in North America of women with suspected preeclampsia. Subjects were enrolled in gestational age blocks between 20 and 41 weeks, and were managed according to local protocols. Final diagnoses were adjudicated by an independent expert panel. Preeclampsia (PE) was defined as Traditional (TrPE, both hypertension and proteinuria, ACOG, 2002), or Revised (RePE, hypertension with either proteinuria or ⩾1 severe feature, ACOG, 2013). Standard definitions of Chronic (CH) and Gestational (GH) hypertension were unchanged. Subjects who did not meet any definition were classified as No Disease (NoD). Results 1223 subjects with signs or symptoms of preeclampsia were followed through delivery. At, enrollment, 980 subjects (80.1%) had hypertension (67% new onset; 33% worsening hypertension) and 602 (49.2%) had new onset proteinuria. 395 (32.3%) reported headaches or visual changes and 80 (6.5%) had RUQ pain. After adjudication of final diagnosis, 120 subjects (9.8%) had GH, 74 (6.1%) had CH, and 199 (16.3%) had NoD. 661 (54.0%) pregnancies met criteria for TrPE, while 794 (64.9%) met criteria for RePE, an increase of 20.1% (p 37 weeks), the number of subjects meeting criteria for preeclampsia increased from 81 (33.5%) with TrPE to 119 (49.2%) with RePE, a 46.9% increase, due primarily to an increase in the prevalence of preeclampsia without proteinuria. Conclusions Redefining preeclampsia by the revised 2013 ACOG criteria will increase the diagnostic prevalence of preeclampsia by 20%. The effect of this diagnostic change on rates of intervention (hospital admission, laboratory testing, and iatrogenic delivery) and prevention of adverse outcome, remains to be determined. Disclosures D. Woelkers: None. J. Barton: None. P. von Dadelszen: None. B. Sibai: None.