The objective of this investigation was to determine the relationship of blood pressure (BP) in young men, ages 20-39 years, to their subsequent BP from the perspective of BP tracking, position in BP distribution and later evidence of hypertensive BP values. Since 1948, the Manitoba Study group has followed 3983 men, 90% of whom were 20-39 years old at entry. BP in persons not prescribed antihypertensive medications was examined at 5-year intervals during the 30-year observation period to 1978. To adjust for age, BP was examined within 5-year age groups at entry. The correlations between entry and subsequent BP at the same length of follow-up were greater for systolic than diastolic BP and increased with older ages. The correlation decreased wtih every 5-year examination after entry for all ages. Men whose BP was below the mean at entry were less likely to have a BP greater than 1 standard deviation (SD) above the mean at any of the examinations. Men with an entry BP greater than 1 SD above the mean were more likely to have BP greater than 1 SD above the mean later, but the relationship decreased considerably after 20 years, especially in 20-24-year age group. The results were similar for the probability of hypertension values (systolic BP greater than or equal to 140 or 150 mm Hg, diastolic BP greater than or equal to 90 or 95 mm Hg) at later examinations. Thus, BP in later life can be predicted from BP at ages 20-39 years and can identify groups at high or low risk for hypertension.