Twenty-two placentas were investigated for the presence and patterns of inflammation by extensive examination, and divided into four groups: 1) term vaginal delivery [group I; n=6]; 2) term cesarean section delivery [group II; n=5]; 3) preterm vaginal delivery [group III; n=4], and 4) preterm cesarean section delivery [group IV; n=7]. In group I, all had deciduitis, and choriodeciduitis/ chorionitis was present in two cases (33.3%). In group II, four cases (80%) showed deciduitis and/or choriodeciduitis/chorionitis; three of these had intact membranes. In group III, three cases (75%) showed deciduitis, and two had chorionitis. In group IV, three cases (42.9%) showed no evidence of inflammation, three had deciduitis and one had deciduitis/chorioamnionitis. In all groups, membranitis was more severe, confined to the inner and mid segments in general, and deciduitis, choriodeciduitis/chorionitis and chorioamnionitis tended to overlap. The study newly demonstrates major characteristics of placental inflammation: higher prevalence and severity of inflammation in the inner segments of membrane and at the periphery of the placenta. Taking this histotopography into account, it is desirable to take sections from the placental margin, and the current concept of placental inflammation as a surrogate marker of intrauterine infection should be reevaluated.