INTRODUCTION: Primary aldosteronism is the most common form of mineralocorticoid hypertension. The disease has been described by Jerome W. Conn in 1955; since that time there has been a great progress in the knowledge concerning the prevalence, diagnostics and treatment of the disease. AIMS: The authors retrospectively analyzed the efficacy of diagnostic procedures and the outcome of treatment by the analysis of data of 187 patients with primary aldosteronism examined between 1958 and 2004 at the 2nd Department of Medicine of Semmelweis University. METHODS: The efficacy of different methods used for the diagnosis, the frequency of the different subtypes of primary aldosteronism, as well as the surgical outcomes in patients with surgically treated subtypes of primary aldosteronism were studied. RESULTS: Aldosterone-producing adenoma was detected in more than two thirds of patients (n = 135), whereas idiopathic hyperaldosteronism was found in 46 patients. Other subtypes of primary hyperaldosteronism occurred less frequently (unilateral primary adrenocortical hyperplasia in 5 patients and adrenocortical carcinoma in one patient). For the diagnosis of familial hyperaldosteronism type I, molecular biological studies of the aldosterone-synthase/11beta-hydroxylase gene chimera were carried out in 30 patients but none of them showed the presence of the chimeric gene. When comparing the clinical parameters of patients with aldosterone-producing adenoma and idiopathic hyperaldosteronism, no significant differences were found in the time period between the diagnosis of hypertension and the diagnosis of primary aldosteronism, or in the systolic and diastolic blood pressure values. The mean of the lowest documented serum potassium concentration was slightly lower in patients with aldosterone-producing adenoma (2.8 +/- 0.1 mmol/l) compared to those with idiopathic hyperaldosteronism (3.1 +/- 0.2 mmol/l), but the difference was not significant. Normokalemic primary hyperaldosteronism was found in 7 cases. The ratio of plasma aldosterone concentration (ng/dl) to plasma renin activity (ng/ml/h) was above 20 in all patients with aldosterone-producing adenoma and in all but 5 cases with idiopathic hyperaldosteronism. To confirm the diagnosis and to differentiate the subtypes of primary aldosteronism, the postural test combined with furosemide administration was performed in the majority of patients. When cases showing an elevation of plasma cortisol level during the test were excluded, this test differentiated patients with aldosterone-producing adenoma from those with idiopathic hyperaldosteronism with a sensitivity of 69% and a specificity of 92%. In cases of adrenocortical adenomas not or not clearly detectable by radiological imaging techniques, as well as in cases with bilateral adrenocortical adenomas, selective adrenal vein sampling was performed (n = 55). All but 4 patients with aldosterone-producing adenoma underwent adrenalectomy. Histology and postoperative hormone results confirmed the preoperative diagnosis in all operated patients. After surgery serum potassium concentration returned to normal in all patients showing low serum potassium levels before surgery. Also, the moderate to severe preoperative hypertension disappeared or improved after surgery. CONCLUSIONS: These observations are in contrast with the results of international studies which showed a high frequency of normokalemic primary aldosteronism and a more frequent occurrence of idiopathic hyperaldosteronism well treatable with aldosterone-antagonists. Therefore, it can be presumed that a significant number of primary aldosteronism cases that are not accompanied with severe hypokalemia remain undetected in Hungary.