The presence of inflammation in decidual and myometrial samples as defined by histopathologic examination and the association between the myometrial inflammation and different maternal infectious morbidity and labor-related clinical variables were evaluated in 648 consecutive women who underwent cesarean section at various gestational periods. Altogether, 1,205 histologic (559 decidual and 646 myometrial) samples were studied. In normal pregnancies, myometrial inflammatory lesions were detected rarely before parturition, indicating their abnormality in these cases. After ruptured fetal membranes with advanced cervical dilatation and in patients with clinical chorioamnionitis, myometrial samples commonly were infiltrated by leukocytes, up to moderate and marked densities. Moderate to marked myometrial inflammation showed no diagnostic value in high-risk term parturients for the prediction of postoperative endometritis. Our study is the first to show the frequency of myometrial inflammation in nonselected consecutive pregnant women and, thus, is important for better understanding the myometrial inflammatory response during human parturition.