Introduction: Hypertension prevalence is increasing worldwide: population ageing and an increase in the prevalence of obesity are contributing to this rise. Hypertension is a major modifiable risk factor for stroke, coronary heart disease, end stage renal disease and has been associated with cognitive impairment. The aim of this study is to determine the prevalence of hypertension and to identify determinants of awareness of hypertension in older Irish adults. Methods: The Irish Longitudinal Study on Ageing (TILDA) is a population based prospective cohort study representative of community living adults. Each member of the Irish population aged 50 years and older had an equal probability of participation in the study. Face to face interviews and objective health assessments were conducted between Oct 2009 and July 2011. Descriptive statistics and logistic regression analysis were used to calculate prevalence and determinants of awareness of hypertension. Survey weights were applied to the estimates to adjust for selection and non-response bias in the survey. Results: The household response rate was 62%. Of the 8,175 respondents who took part in the study 5857 (71.6%) completed a comprehensive health assessment including blood pressure measurement. Hypertension was defined as a mean systolic blood pressure (SBP) ≥140mmHg and/or a mean diastolic blood pressure (DBP) ≥90mmHg and/or currently taking antihypertensive medications. The overall prevalence of hypertension was 64% (95% CI 62-65%) in those aged 50 years and older. Hypertension prevalence was higher in men than in women (69% vs 59%, p<.007) and prevalence increased with age to 87% (95% CI 84-89%) in those aged 75 years and older. Of those classified as hypertensive 55% (95% CI 53-57%) self-reported a previous doctor’s diagnosis of hypertension. Strong determinants of awareness included older age, female sex, overweight and obesity. Conclusions: This study documents a high prevalence of hypertension in adults aged 50 years and older in Ireland and identifies a low level of awareness of hypertension in this group. Raising awareness of hypertension is a major public health challenge. These findings provide reliable information which can contribute to practice and policy aimed at decreasing the prevalence of hypertension.