The objective of this study was to determine the prevalence, treatment, and control of hypertension, and the determinants of undertreatment in the Dutch population. The study design was cross-sectional. A population-based survey on cardiovascular disease risk factors in the Netherlands from 1996 to 2002 was the setting of the study. A total of 10 820 men and women, aged 30-59 years, were included in the study. The main outcome measures of the study were: Prevalence of hypertension, treatment, and control of hypertension and determinants of undertreatment of hypertension. Hypertension was defined as: systolic blood pressure (SBP) > or =140 mmHg and/or diastolic blood pressure (DBP) > or =90 mmHg, and/or the use of antihypertensive medication. Treated and controlled hypertension was defined as SBP <140 mmHg and DBP <90 mmHg. Multivariate logistic regression was used to assess the determinants of undertreatment. The prevalence of hypertension in men was 21.4% and in women 14.9%, and 17.9% of the hypertensive men and 38.5% of the hypertensive women were receiving antihypertensive medication. Of the untreated hypertensives, 21.9% of the men and 13.6% of the women were eligible for treatment with antihypertensive medication according to Dutch guidelines. Female gender and the use of cholesterol-lowering medication were associated with an increased chance of being treated. Subjects who were physically active, on a low salt diet, and current smokers had an increased chance of being untreated. Taking cholesterol-lowering medication and no asthma or allergy were factors associated with better control of blood pressure. In conclusion, a considerable proportion of hypertensives were untreated and uncontrolled. Therefore, the detection and control of hypertension in the Netherlands needs to improve. Several groups of hypertensives were identified that need additional care and attention.