Objective: Our objective was to determine the relative importance of demographic characteristics, clinical risk factors, and ancillary screening tests in the prediction of preterm birth as a result of premature rupture of membranes. Study Design: A total of 2929 women were evaluated in 10 centers at 23 to 24 weeks’ gestation. Demographic and clinical characteristics were ascertained. Cervicovaginal fetal fibronectin and bacterial vaginosis were evaluated. Cervical length was measured by vaginal ultrasonography. Patients were evaluated for spontaneous preterm birth caused by preterm premature rupture of membranes at <37 and <35 weeks’ gestation. Multivariate analyses were performed separately for nulliparous women and multiparous women. Results: Premature rupture of membranes at <37 weeks’ gestation complicated 4.5% of pregnancies, accounting for 32.6% of preterm births. Univariate analysis revealed low body mass index, pulmonary disease, contractions within 2 weeks, short cervix (≤25 mm), positive results of fetal fibronectin screening, bacterial vaginosis, and a previous preterm birth caused by premature rupture of membranes (in multiparous women) to be significantly associated with preterm birth caused by premature rupture of membranes in the current gestation. Short cervix, previous preterm birth caused by premature rupture of membranes in multiparous women, and presence of fetal fibronectin were the strongest predictors for both preterm birth caused by premature rupture of membranes at <37 and <35 weeks’ gestation. Women with positive fetal fibronectin screening results and a short cervix had greater risks both of preterm birth caused by premature rupture of membranes at <37 weeks’ gestation (relative risk, 4.9) and of preterm birth caused by premature rupture of membranes at <35 weeks’ gestation (relative risk, 13.5) than did those without these risk factors. Multiparous women with all three risk factors had a 31.3-fold increased risk of preterm birth caused by premature rupture of membranes at <35 weeks’ gestation. Conclusion: The combination of short cervical length, previous preterm birth caused by preterm premature rupture of membranes, and positive fetal fibronectin screening results was highly associated with preterm delivery caused by preterm premature rupture of membranes in the current gestation. (Am J Obstet Gynecol 2000;183:738-45.)