Systolic blood pressure (SBP) is a more frequent cardiovascular risk factor than diastolic blood pressure (DBP), and has a greater impact on blood pressure staging, though this can vary with age, sex and country. Therefore this paper compares SBP and DBP in terms of community burden and impact on blood pressure staging, among Spain's middle-aged population. Data were drawn from a cross-sectional study on a representative sample of the Spanish population aged 35-64 years. Blood pressure was determined under standardised conditions, and was classified as per WHO-ISH and JNC-VI criteria. Prevalence of SBP > or =140 mm Hg was 34.1%, and that of DBP > or =90 mm Hg, 30.9%. A total of 12% of subjects had isolated systolic hypertension (ISH) and 8.7% had isolated diastolic hypertension (IDH). Of treated hypertensives, 31% had their SBP controlled and 34% their DBP controlled. Of subjects not undergoing antihypertensive drug therapy, 60.8% had congruent SBP and DBP levels, 22.5% were up-staged on the basis of their SBP, and 16.7% were up-staged on the basis of their DBP. SBP alone thus correctly classified JNC-VI staging in 83.3% of subjects vs 77.5% for DBP alone. It was solely among the population >50 years of age, in both sexes, that systolic proved more frequent than diastolic hypertension, ISH greater than IDH prevalence, SBP worse than DBP control, and the percentage of SBP higher than that of DBP up-staged subjects. SBP constitutes a greater community burden than does DBP, and has a greater impact on blood pressure staging in Spain's middle-aged population. However, the differential impact of SBP and DBP upon blood pressure burden and staging is favourable to SBP only among subjects >50 years old. These findings are in accordance with recent guidelines on hypertension management.