A blind histological examination of placentae, with regard to placentitis, was carried out of 2 prospective, selected materials. The first consisted of 283 placentae, which were selected with regard to optimal obstetric outcome. The second consisted of 160 placentae, randomized from all premature and low birth weight infants in the local area. Placentitis was sub‐divided into: funisitis, chorionitis, villitis and hypercellular villi. Funisitis was found in premature infants only. Villitis resulted in the birth of significantly smaller infants and placentae, and must therefore, in contrast to funisitis and chorionitis, be considered chronic. Hypercellular villi are found to have no importance. Funisitis, chorionitis and villitis could possibly be explained by an infection in 10 of a total of 15 cases of placentitis.