BACKGROUND Until recently, primary hyperaldosteronism was considered a rare cause of secondary hypertension. However, in recent years, many studies have suggested that this disease can affect up to 20% of hypertensive individuals. OBJECTIVE To determine the prevalence of primary hyperaldosteronism in hypertensive patients treated at the hypertension league of a university hospital. METHODS Serum aldosterone and plasma renin activity levels were measured in 105 patients while they were undergoing standard antihypertensive treatment, with the exception of those using betablockers and spironolactone, in fasting condition and after rest in the supine position for 20 minutes. Those with an aldosterone/plasma renin activity ratio > 25 were submitted to the saline suppression test and, after the confirmation of the autonomy of aldosterone secretion, a computed tomography of the adrenals was performed. The results are presented as percentages and means and standard deviations. RESULTS Of the 105 patients, 6.54% presented refractory hypertension. Nine presented an aldosterone/plasma renin activity ratio > 25 (8.5% of the total). Of these, 08 were submitted to the saline suppression test and 01 (with refractory hypertension) had the diagnosis of primary hyperaldosteronism confirmed (0.96% of the total). A computed tomography of the adrenals was performed, which showed normal results. CONCLUSIONS The prevalence of primary hyperaldosteronism in the studied sample was 0.96% of the total. However, when only the patients with refractory hypertension were evaluated, the prevalence was 14.3%.