High blood pressure is a modifiable risk factor for cardiovascular disease. Previous studies showing a blood pressure decline in recent decades lack data to follow individuals born in different decades from early and middle adulthood to older age. We investigated changes in age-specific blood pressure by repeated measurements in 37973 women and men born 1905 to 1977 (aged 20–89 years) examined ≤5× between 1979 and 2008 in the population-based Tromsø Study. Mixed models were used to estimate time trends. Mean systolic and diastolic blood pressure decreased from 1979 to 2008 in both genders in the age groups 30 to 89 years. The decrease was similar in the 80th percentile and the 20th percentile of the population blood pressure distribution. The decrease in systolic blood pressure in age group 40 to 49 years was 10.6 mm Hg in women and 4.5 mm Hg in men. Systolic blood pressure increased with age in women and men born 1920 to 1949, whereas a decrease or flattening of curve was observed in the younger birth cohorts. Thus, we found both time periodic and cohort effects, and trends were more pronounced in women than in men. The findings suggest changes in blood pressure in the population rather than an effect of treatment of high-risk individuals.