Objective : The aim of this study was 1) to determine the diagnostic performance of amniotic fluid white blood cell (WBC) count for the antenatal detection of intrauterine infection and 2) to identify the value in prediction of preterm birth and significant neonatal morbidity in patients with preterm premature rupture of membranes. Methods : Transabdominal amniocentesis was done in 255 singleton pregnancies with preterm premature rupture of membranes before 36 weeks of gestational age. Amniotic fluid was cultured for aerobic and anaerobic bacteria and mycoplasmas. Receiver-operator characteristic curve, survival analysis and logistic regression were used for statistical analysis. Results : 1) Prevalence of positive amniotic fluid culture was 19.6% (50/255). Amniotic fluid WBC count was higher in the patients with positive amniotic fluid culture than those with negative amniotic fluid culture (median 269 [0-19764] cells/mm3 vs median 2 [0-7956] cells/mm3, p<0.001). 2) As a diagnostic and prognostic means, the increased amniotic fluid WBC (≥20 cells/mm3) had sensitivity of 74%, specificity of 74%, positive predictive value of 41% and negative predictive value of 92% for the positive result of amniotic fluid culture. 3) An increased amiotic fluid WBC was strongly associated with shorter amniocentesis-to-delivery interval even after adjustment of gestational age at amniocentesis(hazard ratio 3.2736, p<0.0001). 4) Amniotic fluid WBC count was higher in patients with significant neonatal morbidity or congenital neonatal infectious morbidity than those without these (p<0.001 and p<0.005 respectively). 5) Patients with increased amniotic fluid WBC count had higher incidence of significant neonatal morbidity and congenital neonatal infectious morbidity than those with low amniotic fluid WBC count and the association between amniotic fluid WBC and significant neonatal morbidity was statistically significant after adjustment of gestational age at amniocentesis (OR 3.3649, p<0.0001). Conclusion : Amniotic fluid WBC count is of value in antenatal diagnosis of intrauterine infection and prediction of maternal and neonatal outcomes in patients with preterm premature rupture of membranes.