Disorders of sex development are caused by various genetic and environmental factors. Their diagnosis is most frequently made either immediately after birth or in small children and adolescents. These disorders are manifested as ambiguous genitalia, a mismatch between anatomic structures of the internal and external genitals, sex chromosome abnormalities or disorders of gonadal development. The article first discusses normal gender development, with emphasis on molecular and genetic mechanisms. The new nomenclature of disorders of sex development is also presented. One of the most frequent manifestations of these disorders is ambiguous genitalia. Therefore, the final part of the article presents the management of a child with ambiguous genitalia, which serves as an example of complete management of a disorder of sex development. Due to the relative rarity and complexity, a multidisciplinary team of experts must be involved in the management of subjects with this disorder. It is also important to be aware of the relative urgency of these disorders. Furthermore, the course of such disorders may be complicated by acute events, such as electrolyte imbalance and hypoglycemia, especially in newborns and small children.