Fifty years ago, Jerome Conn described 'a new clinical syndrome which is designated temporarily as primary aldosteronism' in a young patient with hypertension, severe hypokalaemia and a benign adrenocortical tumour, for whom an adrenalectomy cured both the hypertension and hypokalaemia. His report identified the condition known as aldosterone-producing adenoma, a form of curable hypertension. According to Conn, the prevalence of primary aldosteronism in the hypertensive population referred to his department was 20%, but this estimate was subject to referral bias. Primary aldosteronism has long been considered rare, with an estimated prevalence of 0.5-2% among unselected hypertensive patients. During the past 10 years, however, the apparent prevalence of the condition increased dramatically, up to 30% in some series. Overall, the prevalence of primary aldosteronism in series dealing with at least 100 screened hypertensive patients averaged 6%, with one patient in two harbouring an aldosterone-producing adenoma. This increase in prevalence reflects the fact that hypokalaemic and normokalaemic patients are now screened for primary aldosteronism, with the aldosterone to renin ratio used as a screening tool. The current 'epidemic' of primary aldosteronism raises several questions and concerns.