Objective: To study the incidence of histological chorioamnionitis (HCA) in term pregnancies according to labor onset. Study design: During 2013–6, term pregnancy placentas were prospectively sent to histopathology evaluation, and compared between patients with spontaneous onset labor, pre-labor ROM, labor induction and elective cesarean deliveries. Results: A total of 260 placentas were obtained, 65 from each group. Rates of HCA for the spontaneous labor, PROM, induction and CD groups were: 49, 32, 24 and 4%, respectively (p < 0.001). Composite neonatal outcome was non-significant between the study groups, and between cases with and without HCA. In a logistic regression model, after controlling for parity - gestational age, mode of delivery, ROM > 12 h and spontaneous onset of labor were found to be independent risk factors for HCA. Conclusion: HCA at term is prevalent in spontaneous labor and supports the association between the inflammatory processes and activation of the physiological signals of parturition.