The presence of female internal genitalia or chromosomes (XX) in conjunction with external genitalia that are ambiguous or male. The preferred term is XX disorder of sex development.

The primary mechanism for this disorder is increased androgen exposure during development. This androgen exposure causes a spectrum of "virilization" of the external genitalia. Signs of virilization are clitoromegaly (sometimes to the point of phallus formation) and labial fusion. The degree of virilization can be rated by the Prader Scale, which incorporates size of clitoris, vaginal and urethral openings, and labial formation.

Excess androgen exposure is often, but not exclusively, from an adrenal source. Congenital adrenal hyperplasia (specifically 21-hydroxylase deficiency) is the most common cause of female pseudohermaphroditism. Rarer causes include androgen exposure through maternal use of certain drugs, androgen secreting tumors, and Y chromosome translocations.