A 36-year-old asymptomatic Chinese male with polycystic kidney disease (PKD) developed hypertension 1 year after the diagnosis of PKD. The patient was treated initially as for hypertension associated with PKD. However, over a 6-year period his hypertension became progressively difficult to control and he developed severe symptomatic hypokalemia. Subsequent investigations confirmed the presence of primary hyperaldosteronism. The initial computed tomographic scans of the adrenals did not reveal any definite adenomas. The patient subsequently underwent bilateral adrenal venous sampling, which suggested a left-sided source of aldosterone excess. A repeat computed tomography of the adrenals with fine cuts revealed a 6-mm diameter adenoma of the left adrenal gland. He underwent an uncomplicated left adrenalectomy. All antihypertensive and potassium supplements were stopped on the 5th postoperative day. Two and half years after the adrenalectomy he remains normotensive and normokalaemic without any medication. The case illustrates the importance of measuring serum potassium before initiation of any therapy and the need to consider secondary causes even if a primary association is known. It also reinforces the fact that when hypertension becomes difficult to control, a secondary cause has to be searched actively. The association between primary aldosteronism and renal cysts has been highlighted only recently. The association of polycystic kidneys and primary aldosteronism has been reported in the literature only once previously.