We describe a patient who was assigned female at birth because of genital ambiguity without performing further diagnostic procedures and presented at the age of 13-1/2 years because of her strong desire to change her legal sex. Karyotype was 46,XY; clinical, endocrinological, radiological and surgical work-up revealed hypergonadotropic hypogonadism and mixed gonadal dysgenesis. Gender identity reversal was performed after extensive psychological testing and adaptation of living circumstances resulting in a successful integration as a male with normal psychological and social functioning. In several surgical procedures, the streak gonad, the nonfunctional testis, and the rudimentary uterus were removed, and a penis was reconstructed from a penisoid with chorda and hypospadias. Our patient supports the idea that gender identity is imprinted prenatally by hitherto poorly understood mechanisms and that sex assignment in infants with ambiguous genitalia needs careful consideration of not solely endocrinological and anatomical data.