BACKGROUND High blood pressure (HBP) is probably one of the main targets for prevention in primary health care. Knowledge of the magnitude and control is needed for monitoring this health problem at the population level. The aim of this study was to estimate the prevalence of hypertension in the adult population of Valencian Region (VR) (Spain), and to evaluate the degree of treatment and control. SUBJECTS AND METHODS Two measurements of blood pressure (BP) were obtained for a representative sample of 1,674 participants (14 years and older) in the nutrition and health survey of the VR in 1994. A semi-automatic digital esfingmomanometer was used. HBP definition was based on the criteria of the WHO and the Fifth Joint National Committee on Detection Evaluation and Treatment on HBP. Criteria of the MONICA project were used to determine the level of treatment and control of hypertension. Prevalence of HBP was estimated for sex and age groups accounting for the study design. RESULTS HBP prevalence was 31.7% (14.1% borderline HBP plus 17.6% defined HBP). Hypertension increased with age from a prevalence of 9.3% in the group 15-24 years of age, to 68.8% in the group > or = 65 years old. A 57% of hypertensive persons were not under treatment, a 16.6% were treated but their BP was not controlled, and a 26.4% were under treatment and presents controlled BP. The uncontrolled BP was more evident at younger ages. CONCLUSIONS This study has shown that one third of the adult population from VR had HBP, and over the half of them are not treated. Furthermore, over one third of hypertensives under pharmacological treatment presented uncontrolled BP. These results should be taken into account if preventive actions are to be implemented at the individual and population level.