Abstract Aim: To assess whether maternal serum C-reactive protein (CRP) and genital mycoplasmas measured can help predict imminent preterm delivery or chorioamnionitis in patients with preterm labor (PL) or preterm premature rupture of membranes (PPROM). Methods: The study group consisted of 165 women with PL or PPROM. Vaginal cultures for genital mycoplasmas and maternal blood for CRP were obtained when they were admitted for the management of PL or PPROM. An elevated level of serum CRP was defined as ≥0.8 mg/dL. Histologic evaluation of the placenta was performed after delivery. Results: The prevalence of positive vaginal fluid cultures for Ureaplasma urealyticum (UU) was 63.0%, and elevated maternal serum CRP was 32.7%. No outcome variables were associated with vaginal UU infection in patients with lower CRP levels. However, among women with elevated CRP, the mean gestational age at birth was significantly reduced, and low Apgar score, neonatal intensive care unit admission, histologic chorioamnionitis, and delivery within 7 days of admission were significantly more common in patients with vaginal UU. Conclusions: Although vaginal UU in PL or PPROM cannot act as the sole predictor of imminent preterm delivery or chorioamnionitis, it can provide predictive information in patients with elevated maternal serum CRP levels.