The clinical significance of completely circumvallate and circummarginate placenta was determined by an analysis of the records of 39,514 obstetric patients and their offspring enrolled in the Collaborative Project The data refute previous studies attesting to the frequent occurrence and serious consequence of extrachorial placenta. Extrachorial placenta was found to be more common in multigravidas. White women with circumvallate placenta had increased rates of antepartum bleeding, prematurity, perinatal, infant, and child deaths, but the stillbirth rate was not augmented. Similar trends were noted in the Negro circumvallate group. Nevertheless, these complications could not be ascribed to abnormal placentation because such problems are more frequent in the black population for other reasons. Even complete circummarginate placenta was not serious clinically in either race.