We report the case of a 42-year-old woman with autosomal dominant polycystic kidney disease complicated by primary aldosteronism. She had a history of hypertension for 12 years and was found to have hypokalemia and polycystic renal and hepatic disease. Endocrinological tests revealed hyporeninemia and hyperaldosteronemia. Adrenal scintigraphy and venography demonstrated a left adrenal adenoma. Blood sampled from the adrenal veins confirmed hyperaldosteronemia originating from the left adrenal gland. Left adrenalectomy was performed. After surgery, plasma renin activity, plasma aldosterone titer, and serum potassium level normalized. The mechanism for the development of primary aldosteronism with autosomal dominant polycystic kidney disease may be related to the activation of the renin-angiotensin system. Four years after left adrenalectomy, hepatic but not renal cysts showed a remarkable increase; the improvement in hypokalemia may have delayed the progression of kidney cysts.