17 alpha-hydroxylase deficiency is a rare form of congenital abnormality in steroid synthesis, usually associated with moderate arterial hypertension and suppression of the renin-angiotensin system in a young adult. We report on a 45 years old woman with malignant hypertension (220/135 mmHg, severe retinopathy with papilledema, progressive renal insufficiency with serum creatinine over 300 mumol/l) of recent onset. Biological exploration revealed a metabolic alkalosis, a moderate hypokalemia (3 mmol/l), with elevated urinary excretion of potassium. Plasma aldosterone concentration (33 ng/dl) and plasma renin activity (17 ng/ml/h) were elevated. Acute captopril administration was followed by a marked (-29 p. 100) decrease in mean arterial pressure. In this 46 XX patient, a primary amenorrhea had never been explored; clinical examination disclosed the absence of female secondary sex characteristics. Plasma cortisol was low (203 mmol/l) as were plasma androgens (testosterone 0.55, androstene dione 0.19, delta HEA less than 0.1 nmol/l respectively) and oestrogens (oestradiol 59 nmol/l). Elevated levels of progesterone and pregnenolone sulfate (12.1 and 2027 nmol/l respectively) contrasted with decreased levels of 17 OH progesterone (0.35 nmol/l). Computed tomography revealed a subnormal right adrenal gland and a pseudo-tumoral aspect on the left side. Treatment with dexamethasone and combined antihypertensive drugs (captopril, nifedipine and atenolol) resulted in normalisation of blood pressure and secretion of renin and aldosterone but renal function did not fully recovered. Thus, the hypertension of 17 alpha-hydroxylase deficiency can follow a malignant course in association with a marked activation of the renin-angiotensin system.