Primary aldosteronism is a disease that the stimulus for the excessive aldosterone production residues within the adrenal gland. It was first described by conn in 1955. And many cases were reported by physicians at present in the world. But it is relatively rare in Korea, probably due to lack of attention and medical facilities. Only about 13 cases have been reported at present. The clinical, biochemical feature in l case of primary aldosteronism caused by adrenal hyperplasia that was diagnosed at Yeungnam University Hospital was observed and the following result were obtained. 1. Clinical feature: The present case was 27-year-old woman who was admitted due to general weakness and easy fatigability. The above mentioned chief complaints occurred 8 months prior to admission when she delivered of second baby by cesarean section. Symptoms such as above chief complaints, intermittent muscle paralysis and cramping were noticed. Trousseau's sign was also present. The average blood pressure ranged from 170/90 to 200/120 2. Biochemical abnormalities: Severe hypokalemia lower than 2.5 mEq/L was presented and 24 hours urine potassium showed markedly increased urinary loss (228 mEq/day). Plasma rennin activity was decreased under normal range with furosemide administration. (Basal renin; 0.01 ng/ml/hr, stimulated rennin 0.12 ng/ml/hr). Saline suppression test revealed markedly elevated levels of aldosterone higher than normal range (Basal aldosterone; 320.68 pg/ml stimulated aldosterone; 451.86 pg/ml). And posture test showed decreased plasma rennin activity and increased plasma aldosterone level. 3. Adrenal CT scan revealed no abnormal findings. 4. Treatment and course: Spironolactione was given at OPD with regular follow-up. Her blood pressure ranged from 150/90 to 160/100 and symptoms were improved. The effect of treatment was satisfactory and further follow up would be performed.