[Diagnosis and management of 46,XY mixed gonadal dysgenesis and disorder of sexual differentiation]. 
We present our experience in diagnosing, gender assignment, and surgical management of sexual ambiguity in 46,XY mixed gonadal dysgenesis.  A retrospective study of five cases treated from 2003 to 2006 was performed.  Clinical picture, operative findings, testosterone levels, and immunohistochemistry of gonads for the expression of FOXL2, SOX9, AMH, AMHr, C-kit, and PLAP were analyzed.  All patients had ambiguous genitalia, urogenital sinus, uterus, testicle on one side, and a streak gonad on the other.  Four patients were reared as male and one as female.  Stimulation by human chorionic gonadotropin showed good penile size and testosterone response.  All patients underwent laparoscopic gonadal biopsy and/or gonadectomy.  Histological studies showed the presence of sparse primordial follicles surrounded by embryonic sex cords in the streak portion of gonads.  Germ cells were C-kit positive in all and PLAP positive in four patients.  FOXL2 expression was detected in four streak gonads and in none of testes.  AMH expression was found only in testes.  SOX9 expression was found in both investigated testes and in three out of four streak gonads investigated.  46,XY mixed gonadal dysgenesis should be differentiated from ovotesticular and other types of 46,XY disorders of sexual differentiation by the typical gonadal histology and internal genital structure.  High testosterone level after stimulation and good response to testosterone treatment in 46,XY mixed gonadal dysgenesis could orient toward male sex assignment.  There are different patterns of gene expression in testicular and streak gonads with a switch to FOXL2 positivity in streak gonads.  Early gonadal and genital surgery is recommended.