A study has been made of a prospectively selected material of circumvallate placentae; the latter being defined as an elevated edge of more than 50% of the circumference. The material consists of 447 placentae from liveborn singleton infants, where 287 were from exemplary pregnancies, and 160 from births with a gestational age (GA) of less than 266 days and/or a birth weight of less than 2 750 g. The material was prospectively randomized. It was divided into clinical groups according to the GA and under‐weight. Nineteen circumvallate placentae were found. Among these were more multigravidae and more with pre‐gestational menstrual irregularity than expected. The number of antepartum haemorrhages was as expected. There were more premature infants, premature under‐weight infants and under‐ weight infants than expected. Nine of the 20 premature under‐weight infants in the material had circumvallate placenta. In relation to a previously published basic material, it was found that the birth weight, and placental content of RNA and DNA were significantly reduced. It is concluded that placentae with more than 50% circumvallation are associated with prematurity and under‐weight, as well as a placenta with fewer cells than normal. The genesis of the anomaly is discussed.