Secular trends in blood pressure among young adults reflect the proportion of the population at risk of developing hypertension and may be markers of progress in primary prevention. National health examination data from three successive surveys were analyzed to assess blood pressure trends for adult blacks and whites aged 18-34 years in two body mass index (BMI; weight (kg)/height (m)2) strata (< 25 or > or = 25). Blood pressure was categorized into a four-point ordinal scale using the weighted, within-sex 50th, 75th, and 90th percentiles for 18- to 24-year-old adults in the 1960-1962 survey. The effects were analyzed with cumulative logit models with alpha = 0.01. The systolic blood pressure decreased moderately for 25- to 34-year-old males and for females except those aged 25-34 years with a BMI of > or = 25. Diastolic blood pressure increased among males with a BMI of > or = 25 and among white males with a BMI of < 25, but did not show a significant overall trend among females. A BMI of > or = 25 was associated with substantially higher blood pressure in each survey, except for one age-sex-race subgroup. Racial differences within BMI were less consistent than the differences across BMI strata. In summary, the situation with respect to hypertension among females may have improved during this time period but for males may have worsened with respect to diastolic blood pressure. Data for both sexes support a need for population-wide obesity prevention to reduce the incidence of hypertension.