We report the case of a 34-year-old woman with autosomal dominant polycystic kidney disease associated with primary aldosteronism due to left adrenal adenoma. Although autosomal dominant polycystic kidney disease could mask hypokalemia and hypertension, refractory hypertension and hypokalemia were the clues that led to this diagnosis. The diagnosis of primary hyperaldosteronism was based on the presence of hypokalemia with excessive urinary potassium excretion and characteristic hormonal changes. Under laparoscopy, left adrenalectomy was performed. After surgery, plasma renin activity, plasma aldosterone titer, and serum potassium level normalized with only partial correction of the blood pressure. This could be explained by the persisting underlying polycystic kidney disease. We conclude that extrarenal causes in a hypertensive and hypokalemic patient with polycystic kidney disease may be ruled out.