Primary aldosteronism is due to either a unilateral adrenal adenoma or bilateral hyperplasia of the adrenal cortex in most cases. A unilateral adrenalectomy in hypertensive and hypokalemic patients, with a well-documented adrenal adenoma, is usually followed by the correction of hypokalemia in all subjects, with the cure of hypertension in 60 to 87% of patients. Here, a unique case, in which a unilateral adrenalectomy for the removal of an adrenal adenoma was followed by severe hyperkalemia, low levels of plasma renin activity and serum aldosterone, suggestive of chronic suppression of the renin-aldosterone axis, is reported. In a follow-up Lasix stimulation test on the 70th day after surgery, the suppression of the renin-aldosterone axis was resolved, indicating the suppression was transient. Patients undergoing a unilateral adrenalectomy for an aldosterone-producing adenoma should be closely followed up to avoid severe hyperkalemia.