Leading symptoms of 17-hydroxylase/17,20-lyase deficiency in childhood are hypertension and hypokalemia. We found this enzyme defect in 3 phenotypically female siblings aged 12, 15 and 16 years. Two of the sibs have a 46,XY chromosome pattern, the third is genetically female. Pubertal development did not occur. Both of the 46,XY sibs have male internal and female external genitalia. The 46,XX sister has normal female internal genitalia. At the time of diagnosis, two of the three siblings had hypertension (RR between 190/135 and 160/110 mmHg). Two of the three siblings had low serum potassium and metabolic alkalosis. All three patients had excessively high plasma levels of 11-deoxycorticosterone (DOC) and corticosterone. Aldosterone was also elevated whereas plasma renin activity was suppressed. Plasma cortisol and its 17-hydroxylated precursors were low, as were plasma testosterone, dihydroepiandrosterone sulphate and estradiol, while the gonadotropins LH and FSH were elevated in all three patients. We studied the steroid profiles of these three patients during long term glucocorticoid treatment with dexamethasone, which is now followed for 13 years. Blood pressure and serum potassium became normal. Plasma aldosterone, corticosterone and DOC were clearly lower but not fully normalized. The two genetically male sisters obtained estrogens for induction of female secondary sex characteristics. The third 46,XX sister has normal menstruations during substitution with cyclic estrogen/gestagen therapy. All three patients lack pubic and axillary hair, and reached normal adult heights both for phenotypic sex and for target height. The psychosocial orientation is female in all of them. Apart from rare reports of development of malignant hypertension, prognosis is better than in other enzyme deficiencies causing congenital adrenal hyperplasia since no Addisonian crises occur due to DOC and corticosterone overproduction resulting in apparently normal endogenous glucocorticoid activity.