Because of the paucity of serial blood pressure data on the same individuals, little is known about the accuracy of elevated blood pressure (BP) in childhood for predicting hypertension (HBP) later in life. The availability of long-term serial BP data from the Fels Longitudinal Study (FLS) presents the opportunity to link HBP in adulthood directly to BP measured decades earlier in the same individuals as children. We analyzed serial data from 965 men and 1114 women in the FLS. We used an autoregressive-moving average (1, 1) [ARMA (1, 1)] longitudinal model to predict adult HBP from childhood values. For 15-year-old boys with SBP 15 mmHg and 30 mmHg above the average SBP of 90 mmHg, the probabilities of having HBP at age 35 are 0.18 and 0.33, respectively. The corresponding probabilities for 15-year-old girls are only 0.04 and 0.08. This striking sex difference in risk of HBP at age 35 between 15-year-old boys and girls indicates that the risk of developing HBP in women is low regardless of their childhood blood pressure at any age from 2 to 17 years. Men are about 4.25 times more likely to have HBP at age 35 than women over a range of SBP of 90 - 140 mmHg at age 15. The ARMA (1, 1) model allows the identification of boys at risk for HBP as adult men.