Studies examining the use of C-reactive protein (CRP) as a predictor of chorioamnionitis in preterm prelabour rupture of membranes (PPROM) report highly conflicting results. Despite this, CRP is commonly used for the early diagnosis of chorioamnionitis. To determine the diagnostic accuracy of CRP in the detection of chorioamnionitis in women with PPROM. Systematic review. Studies were identified from MEDLINE (1966-2006), EMBASE (1974-2006), PubMed and the Cochrane Library (2005) and from reference lists from primary studies and reviews. Only studies of good methodological quality that evaluated the diagnostic performance of CRP in chorioamnionitis in women with PPROM were selected. Positive and negative likelihood ratios (LR) and diagnostic odds ratios (DOR) were calculated. An attempt was made at pooling data for meta-analysis, but this was considered inappropriate due to the significant unexplained heterogeneity between studies. There were eight primary studies comprising 610 cases which met the inclusion criteria. There was wide variation in the positive and negative LR and DOR between the studies, with significant lack of precision demonstrated by wide confidence intervals. Three of the studies concluded that CRP was a useful diagnostic tool for chorioamnionitis (DOR ranging from 4.2 to 191.6), although one of them suggested a higher CRP threshold. The other five studies concluded the opposite (DOR ranging from 1.4 to 17.7). There is no clear evidence to support the use of CRP for the early diagnosis of chorioamnionitis. Further research is required to address the contradictory findings of diagnostic accuracy.