The simplest response to the question, what is the prevalence of hypertension in the United States today?, is given by a currently popular slogan: ‘23,000,000 Americans have hypertension’. It is clear that the problem is large in scale, but this figure alone is an insufficient guide to many practical issues. The prevalence ratio underlying this estimate is about 15% for adults 18 to 79 years of age. Actual prevalence ratios may vary widely in specific subgroups of the population and in accordance with differing methods and criteria of ascertainment. For example, the actual numbers of hypertensives in the general population of the US, detectable by twostage screening, may be closer to 8 or 9 million. On the other hand, the current failure generally of detection of hypertension would suggest that the entire adult population must be screened periodically–and this number is greater than 126 million. The implications of these considerations for undertaking screening and management programmes are discussed briefly.