OBJECTIVESL: To summarize the clinical characteristics of partial 17alpha-hydroxylase/17,20-lyase deficiency (17OHD) in 46,XX Chinese patients. METHODS: Five cases of 46,XX partial 17OHD from Peking Union Medical College Hospital were studied retrospectively by summarizing and analyzing their clinical data. The molecular pathogenic mechanisms involved are discussed after reviewing the literature. RESULTS: Both complete and partial 17OHD patients have hypergonadotropic hypogonadism and elevated serum levels of adrenocorticotropic hormone and mineralocorticoids. The clinical characteristics of partial 17OHD are different from those of complete 17OHD; patients with the former having various degrees of estrogenic and androgenic impacts such as the development of breasts and pubic hair, and oligomenorrhea or secondary amenorrhea. Elevated serum progesterone with or without elevated serum 17alpha-hydroxyprogesterone and recurrent ovarian cysts are typical manifestations of partial 17OHD. Furthermore, hypokalemic hypertension may be absent in partial 17OHD. The 46,XX partial 17OHD should be differentiated from pure gonadal dysgenesis, premature ovarian failure and polycystic ovarian syndrome. It has been reported that specific mutations of the CYP17 gene can cause partial loss of 17alpha-hydroxylase/17,20-lyase activities or dissociation between the 17alpha-hydroxylase and the 17,20-lyase functions. Oral contraceptive pills are effective for artificial menstruation, but not for the correction of hormone deficiency. A low dose of cortisol should be prescribed in the presence of hypokalemic hypertension. CONCLUSION: The congenital partial 17OHD should be included in the differential diagnosis of menstrual disorders. In these cases, elevated progesterone offers a valuable clue for further investigation.