Mixed gonadal dysgenesis (MGD) is a form of sex chromosome disorder of sex development with large phenotypic variability. Patients with MGD typically have asymmetric and ambiguous genitalia with a combination of Müllerian and Wolffian duct derivatives. Prenatal androgen exposure results in variable degrees of phallic enlargement and a urogenital sinus. Here, we report an infant with ambiguous genitalia due to MGD. Despite marked evidence of prenatal androgen exposure, there was a completely intact distal vagina.Keywords disorder of sex development; mixed gonadal dys-genesis; urogenital sinus Case reportA term infant was born with ambiguous genitalia consisting of a 2.0×0.8 cm phallic structure with chordee, non-palpable gonads, separate vaginal and urethral openings, and prominent rugated labioscrotal folds ( Figure 1A). Testing for congenital adrenal hyperplasia was negative. Müllerian inhibiting substance (MIS) was 33.6 pmol/L (RR for males: 111-348 pmol/L; females: <51 pmol/L). Testosterone at baseline was 0.2 nmol/L and increased to 3.1 nmol/L following an hCG stimulation test (male RR: 6.2-25.5 nmol/L). FSH at 13 days indicated primary gonadal dysfunction. A peripheral karyotype was 45,X/46,XY, consistent with mixed gonadal dysgenesis (MGD). The patient's laboratory data are summarized in Table 1.