Primary hyperaldosteronism (PHA) is one of the leading causes of persistent hypertension. In this paper, we report the case of a 57-year-old woman who presented at our emergency department (ED) with muscle weakness and persistent hypertension. The initial examination revealed high blood pressure (232/136 mmHg), muscle weakness, hypokalemia (K+=2.1 mEq/L), and metabolic alkalosis (pH=7.47). Initial ED therapy failed. Because persistent hypokalemia and arterial hypertension with metabolic alkalosis raised the suspicion of PHA, we obtained measurements of renin activity (0.3 ng/ml/h, normal values: 0.2-2.8 ng/ml/h), aldosterone concentration (534.41 pg/ml, normal values: 10-160 pg/ml) and the ratio of aldosterone concentration/renin activity (178 ng/dl/ng/ml/h). There was no surrenal adenoma on the abdominal computerized tomography. The patient was administered a daily 100 mg dose of aldactazide. At the end of two weeks, the patient was discharged with normal blood pressure and K+ level. PHA is one of the leading causes of persistent hypertension. The emergency physician should pay close attention to patients with hypokalemia and metabolic alkalosis accompanying symptoms such as persistent hypertension, in order to diagnosis PHA early and reduce cardiovascular complications.