The exact pathogenesis of prematurity and intrauterine growth retardation (IUGR) is still obscure in detail. Histological examination of placental tissue may be helpful. In a retro- and prospective study we examined 212 placentas including eutroph-term (n = 80 as controls), hypotroph-term (n = 68), eutroph-preterm (n = 53) and hypotroph-preterm (n = 11) deliveries, respectively. Placentas of the control group showed a significant higher weight, a higher utero-placental diameter and a smaller thickness. We observed villous dysmaturity in a significant higher frequency in risk groups, compared with controls (70-80% vs. 15%). Retarded villous maturity occurred in 38.2% in the hypotroph-term group and in 36.4% in the hypotroph-preterm group, respectively. Placentas of eutroph-preterm deliveries showed a prematurity of the villous tree in 47.2% Our own results and data from literature suggest, that the majority of prematurity and IUGR is not caused by placental dysmaturity itself. Fetal hypotrophy is sometimes caused by inadequate adaptation of the placental tissue due to a virtual slowly appeared disturbance, probably in the uterine maternal blood flow. After the adaptation of placental tissue the organ is able to secure the fetal nutrition supply. A second "hit", e.g. inflammation of the chorion may lead to prematurity. If the compensation of the dysbalance between fetal nutrition-supply and placental capacity is impossible the birth of a premature fetus, mostly dysmature, takes place.