Testicular dysgenesis derives from abnormal gonadal differentiation caused by sex chromosome abnormality. Individuals with sex chromosomal mosaicism manifest diverse phenotypes from phenotypic females and individuals with mixed gonadal dysgenesis (MGD) to males. Gonadal asymmetry in MGD is cytogenetically due to local prevalence of cell lines carrying different karyotypes; XO in the streak gonad and XY in the dysgenetic testis while sex chromosome abnormalities in blood do not always reflect the genital abnormalities. Gender assignment should be based on the potential for normal function of the external genitalia under the parents agreement. Laparoscopic and microscopic surgery facilitates the diagnosis and treatment in infants with MGD and its variants. Close follow-up is mandatory for detecting the highly prevalent gonadal tumor in male subjects.