The study "Successive Small-for-Gestational Age Births" (SGA study) was initiated and is sponsored by the National Institutes of Health (N.I.H.) in the U.S.A. Its purpose is to describe and characterize the different types of intra-uterine growth retardation and their consequences, to assess the associated risk factors, and to provide a basis for preventive measures. Starting in 1986, it runs concurrently in Bergen and Trondheim (Norway), Uppsala (Sweden) and Birmingham, Alabama (U.S.A.), recruiting pregnant para 1 and 2 mothers at high risk of having an SGA birth and a random (control) sample of the total pregnant population. Data collection will end in late 1989, when the last-born children have reached 13 months of age. At the present symposium, investigators from all four study centers and the N.I.H. described the study design and discussed problems of methodology. Strict standardization of parameters to determine gestational age (ultrasound, menstrual dates) is a prerequisite for comparison of results over time and between study centers. Some preliminary results were presented.