The CASTEL (CArdiovascular STudy in the ELderly) has been performed in order to evaluate the prevalence of hypertension of people aged 65 years or more, to evaluate the cardiovascular risk of elderly subjects from a general population, to verify the feasibility and effectiveness of a systematic continuous community-based hypertension control program in the elderly, and finally to evaluate whether a population-based therapeutic intervention was able to extend to a great number of elderly hypertensive patients the benefits of a better control of hypertension. Only the preliminary results of the initial survey are described in this paper, since the final data collection will be available at the end of 1991. The prevalence of hypertension in elderly subjects of the CASTEL was 51.2% (44.6% for males, 52.2% for females), that of isolated systolic hypertension was 8.8% among the whole population sample (2254 subjects) and 23.4% among the subgroup of 850 hypertensives screened following the WHO criteria; 8 visits were performed during the initial screening and prevalence of hypertension regularly decreased from the first visit to the last one. Taking into consideration the mean of the last 2 blood pressure measurements performed during visit 8, average systolic blood pressure was 175.5 +/- 25.9 mmHg and diastolic 93.5 +/- 13.0 mmHg. Some correlations between blood pressure and other biological parameters are also discussed.