Background. Primary aldosteronism (PA) is an adrenal disorder which is characterized by the overproduction of the mineralocorticoid hormones by the adrenal glands when not as a result of excessive renin secretion. Different studies report the prevalence of PA in from 7 to 15% patients with hypertension. Nowadays PA is considered to be the most frequent cause of secondary hypertension taking up to 30% of it. The importance of case detection of PA among hypertensive patients is not a matter of controversy presently. It has been demonstrated recently that patients with PA are more prone to cardiovascular events and target organ damage than essential hypertensive patients. Aim — to establish renal dysfunction in PA. Material and methods. We evaluated 192 low-renin hypertensive patients and 30 normotensive subjects. The mean age of the hypertensives was 47.5±3.4 years. The control group was 51.8±4.2 years old. PA was established in 57 patients, all the others were classified as low-renin essential hypertensives (LREH). Both groups were similar with respect to age (44.7±4.2 in PA, 48.3±3.9 in LREH), sex (female 63% of PA and 67% of LREH) and blood pressure (158±16/96±8 mm Hg in PA, 164±21/99±13 mm Hg in LREH). There were slight differences in BMI (31.4±4.3 in PA and 28.7±3.5 in LREH; p<0.05). PA and LREH patients significantly differed with respect to prevalence of diabetes mellitus (26.3% in PA and 9.6% in LREH; p<0.01) and duration of hypertension (7±5 years in PA and 13±4 in LREH; p<0.05). Results. We observed an increase in urinary protein excretion in both group. But in group of patients with PA it was higher than in LREH (0.14±0.06 vs 0.05±0.03 g/24 h; p<0.05). In addition, patients with PA had higher serum creatinine concentrations (101.7±13.2 vs 83.4±9.1 mkmol/l; p<0.05). Subgroup analyses of normoglycemic subjects showed that PA patients still had a higher creatinine concentration (84.3±11.8 vs 81.9±10.5 mkmol/l) but the difference was no longer statistically significant. Although, microalbuminuria was significantly higher in non-diabetic PA patients (0.12±0.04 vs 0.05±0.07 g/24 h; p<0.05). Diabetic subjects in both groups did not differ significantly with respect to microalbuminuria. Conclusions. Cross-sectional Primary Aldosteronism Prevalence in Italy (PAPY) study showed an increased prevalence of microalbuminuria in PA. The data from German Conn’s Registry showed a significant increase of serum creatinine concentrations in patients with PA but they did not observe any significant differences in protein excretion. In our study the differences in creatinine concentration were diabetes-dependent. Although, we suppose an increase of microalbuminuria in patients with PA to be aldosterone-dependent. However, this hypothesis should be confirmed in wider populations.