National perinatal mortality data suggest that the root causes of many deaths may lie in the environmental circumstances in which the mother grew up. Aberdeen primigravidae under the age of 20 years who gave birth to a baby with a birthweight of less than 2500 g between 1968 and 1972 were divided into those where there was an associated obstetric complication and those where the cause of the low birthweight infant was 'unexplained'. The 'unexplained' group were more often smaller, underweight, cigarette smokers, and from relatively large families in the lower socioeconomic classes. Investigations of case records and by interview revealed that the mothers of these primigravidae were similarly disadvantaged and it is argued that further improvement in perinatal health and mortality will depend on the elimination of this continuity of social disadvantage.