ObjectivesTo examine the interplay between childhood growth and living conditions in the development of hypertension.DesignA longitudinal study of people whose growth between birth and 12 years, and social circumstances during childhood and adult life, were recorded.SettingHelsinki, Finland.ParticipantsEight thousand seven hundred and sixty men and women born in Helsinki University Central Hospital during 1934–44, who attended child welfare clinics in the city and were still resident in Finland in 1971.Main outcome measuresIncidence of hypertension defined by prescription of medication.ResultsThe 1404 children who later developed hypertension grew differently to other children. Low birthweight and shortness or thinness at birth were followed by rapid compensatory growth in weight and height, and an above-average body mass index (BMI, kg/m2) from the age of 8 years onwards. Some 25% of children with low birthweight but high BMI at 12 years subsequently developed hypertension, compared to 9% of those with high birthweight but low BMI. Growth had large effects on the risk of later hypertension in children living in poor social conditions, but only small effects in children in good living conditions. Living conditions in adult life did not affect the risk of hypertension.ConclusionsHypertension originates in slow fetal growth followed by rapid compensatory growth in childhood. This path of growth has a greater effect on the risk of disease among children who live in poor social conditions. Living conditions in adult life do not seem to be important.