“Sex”is defined by several factors, such as chromosomes, gonads, and internal and external genitalia. Males basically have a Y chromosome and testes. The testis produces and secretes Mullerian inhibiting substance and testosterone. These two factors induce internal and external genitalia to develop into the male phenotype. The degree of sexual differentiation relates to the levels of Müllerian inhibiting substance and testosterone. The treatment strategy for patients with sexual differentiation should be decided based on the degree of abnormality of internal and external genitalia.