In 9596 patients followed throughout two pregnancies, recurrence of intrauterine growth retardation (IUGR) was evaluated as a function of previous birth weight percentile and attendant complications of pregnancy. Among 4623 patients with two uncomplicated pregnancies, the prevalence of recurrent IUGR was significantly related to the severity of growth retardation in the first pregnancy (P less than .0001). Those patients with both medical complications and IUGR in the first pregnancy remained at significantly increased risk for recurrent IUGR, even when the second pregnancy was uncomplicated. In second pregnancies, the combination of a previous history of an IUGR neonate and an additional current complication of pregnancy acted synergistically to increase the risk of recurrent IUGR to a level higher than that attributable to either risk factor alone.