The results of the investigation of all 238 immature deliveries (second-trimester abortions) that occurred in the period 1973 to 1985 in the Academic Hospital of the Vrije Universiteit in Amsterdam are presented. The incidence after 1979 was found to be increasing. Excluding all deliveries with a known cause, 126 'idiopathic' cases remained. In these, the obstetrical history of the women revealed a tendency to recurrent pregnancy wastage. The pregnancies frequently showed growth retardation of both fetus and placenta. Therefore, an extensive search for possible causes and an accurate evaluation of fetal development during a following pregnancy is advocated.