A longitudinal study of juvenile hypertension made possible to investigate after 20 years 73% of a group of young hypertensives (original age 14--29 years, arterial blood pressure 170/100 and higher 20 years ago), which was originally investigated in 1952--1954. The surprising result was that 35.5% had a normal blood pressure without treatment in the interval, 40.2% showed the same level of hypertension, 5.7% showed higher blood pressure levels but without any new organic changes, 1.5% had the same blood pressure as 20 years earlier, but now required drug therapy as opposed to previously. Only 17.1% of the patients showed any convincing evidence of progression of the disease, i.e. the development of new organic changes. The prognosis of moderate hypertension at a young age is significantly correlated with: a) the occurence of hypertension in the parent; b) the life expectancy of the parents; and c) the initial values of blood pressure. There was no correlation between prognosis and over-weight, weight gain in the past 20 years, original or present heart rate, smoking, alcohol intake or physical activity, participation in sports or the living standard of the given individual.