Ambiguous genitalia in the newborn is an emergency requiring a multidisciplinary approach to diagnosis and management. The differential diagnosis includes gonadal differentiation disorders, female pseudohermaphroditism, and male pseudohermaphroditism. The initial evaluation includes a history, physical examination, radiologic studies, and a karyotype, with subsequent specifically directed laboratory tests. Gender assignment involves consideration of future sexual functioning, fertility, and physical appearance. The information required to assign sex of rearing is usually available within 48 to 72 hours of birth. Management involves ongoing medical follow-up, timely surgical repair, and psychological counselling as needed. Parents require education with respect to sex differentiation and the specific disorder of their child. Normal psychosocial development is dependent on parents' confidence in their ability to raise their child according to the assigned sex.