Altogether 379 men of the same age have been followed for more than 40 years, mainly as regards socioeconomic conditions during the first 10 years as well as cognitive ability measured at the ages of 10 and 20, education, income development, and psychosocial conditions in adulthood. At the age of 48 a health investigation was performed. In order to identify possible risk factors associated with the development of raised blood pressure 38 subjects with essential hypertension were compared with 155 men without any obvious mental or somatic diseases. No differences regarding socioeconomic conditions during childhood could be observed between the two groups. However, there was a very strong difference between father's education and the son's cognitive ability in the group with hypertension. The low income development for the group with hypertension can probably be explained partly by the lower cognitive ability. In the total group there was a positive correlation between IQ at the age of 10 and income at the age of 43 (r = 0.42; p less than 0.001). The hypertensive men were psychosocially disadvantaged with respect to divorce rate and job dissatisfaction, and furthermore they reported low physical activity during leisure time. Hypertensive men were more obese and had inferior respiratory function. The observation that a lower cognitive ability seems to be related to the development of hypertension is compatible with the observation that early mortality in this investigated group has a correlation of a low IQ with poor socioeconomic conditions in childhood.