Adrenal tumours incidentally found in patients with arterial hypertension pose a severe clinical problem when no endocrine hyperactivity is confirmed and their features in diagnostic imaging do not suggest malignancy.The aim of the study was to evaluate the clinical consequences of unilateral adrenalectomy in a long term follow up period for patients that have adrenal tumours without confirmed endocrine hyperactivity.Material and methods. We evaluated the clinical consequences of unilateral adrenalectomy in a long term follow up of 48 hypertensive patients with a unilateral adrenal tumour lacking biochemical confirmation of adrenal hyperactivity. The mean duration of hypertension was 87 months; observation time ranged from 6 to 62 months.Results. Normalisation of blood pressure was observed in 8.3% of patients. In addition, better blood pressure control was documented in 35.4% of patients. There were no significant differences between group of patients with normalization or improvement of blood pressure control and those with no improvement with respect to age, BMI, duration of hypertension, tumour size, renin activity, aldosterone to plasma renin activity ratio, or the preoperative plasma concentration of potassium, aldosterone, or cortisol. The maximum values of systolic, but not diastolic, blood pressure before surgery were lower in patients with normalization or improvement of blood pressure control.Conclusions. Improvement of blood pressure control after unilateral adrenalectomy in 43.7% of patients may suggest tumour endocrine hyperactivity which remains unconfirmed by laboratory tests. It is not possible to predict improvement of blood pressure control after adrenalectomy in this group of patients according to tumour size and routine biochemical examination.