The aim of the study was to evaluate the possible changes in plasma adrenomedullin (AM) levels in patients with primary aldosteronism before and after surgical resection. The study included 13 patients affected by aldosterone-producing adenoma (9 women, 4 men; mean age 36.2+/-14.2 years) and 20 healthy control subjects (7 women, 13 M; mean age 31.8+/-12.4 years). Unilateral adrenalectomy was performed in all patients and adrenal mass consisted of a benign adrenal cortical adenoma. The mean plasma AM concentrations in patients with primary aldosteronism (36.2+/-19.3 pg/ml) were significantly (p < 0.0001) higher than those of normal subjects (13.2+/-6.2 pg/ml). In these patients the plasma AM levels significantly (p < 0.0001) reduced after surgical removal of the tumours (14.9+/-7.6 pg/ml). In all patients with aldosterone-producing adenoma, tumour diameter correlated with the plasma AM concentrations (r=0.631; p < 0.021). In conclusion, the present investigation shows that in primary aldosteronism due to adrenal adenoma plasma AM levels are higher at the moment of diagnosis and decline after successful adrenal operation.