BACKGROUND : 17α-Hydroxylase deficiency is a recessively inherited autosomal disease caused by mutations in the CYP17A1 gene. It is a rare disease and accounts for approximately 1% of congenital adrenal cortex hyperplasias. Inhibition of 17α-hydroxylase causes low levels of cortisol and high levels of adrenocorticotropic hormone in the blood as well as excessive levels of mineralocorticoids that lead to hypertension and hypokalemia. Usually, the female patients are diagnosed with abnormality of the genitalia or extra genitalia, primary amenorrhea, or hypertension in puberty. We report a case of a 29-year-old woman who had undergone gonadectomy in her childhood due to complete androgen insensitivity syndrome and was diagnosed with 17α-hydroxylase deficiency in adulthood. METHODS : Our patient was a Japanese female diagnosed with androgen insensitivity syndrome, and both gonadectomy and episioplasty were performed at the age of 11 years at the University of Tsukuba Hospital. Thereafter, she was transferred to our hospital at the age of 21 years for vaginoplasty. At the age of 25 years, she presented with hypertension followed by complicated hypokalemia at the age of 28 years. The captopril loading test and adrenocorticotropic hormone loading test of her adrenal steroidogenesis revealed primary aldosteronism. After sufficient genetic counseling, a genetic test was performed that identified her as having CYP17A1 gene mutation. CONCLUSIONS : The differential diagnosis of disorders of sex development can be difficult at a young age without complete expression of the phenotype. However, diagnosis at a later age would change the treatment and prognosis of the disease; therefore, a genetic examination should be considered.