Trends in systolic blood pressure, 24-hour sodium excretion, and stroke mortality in the elderly in Belgium. Data from six surveys of systolic blood pressure conducted in Belgium between 1967 and 1986 were analyzed. The mean ages of the six groups of 3,328 subjects ranged from 70 to 81 years. The prevalence of systolic blood pressure levels above 159 mm Hg decreased between 1967 and 1986 from 51% to 21% in men and 66% to 22% in women; severe hypertension (systolic blood pressure greater than 220 mm Hg) nearly disappeared. During the same period, body mass index increased 1.1 kg/m2 in men and was unchanged in women; mean systolic blood pressure decreased from 159 to 142 mm Hg in men and from 171 to 147 mm Hg in women; the proportion of subjects receiving treatment for hypertension increased from 10% to 36% in men and from 18% to 41% in women; and the mean standardized 24-hour sodium excretion decreased from 265 to 188 mmol in men and from 208 to 160 mmol in women. Systolic blood pressure levels were significantly and independently related to sodium excretion in the 1967 and 1972 studies. The decrease in systolic blood pressure in Belgium was influenced by the combined effects of more and better treatment for hypertension and a decrease in sodium intake. 