The aetiology of disorders of sex development (DSD) is multifactorial and includes chromosomal defects, developmental abnormalities of the gonads, and defects of hormonal synthesis and expression. Infants born with ambiguous genitalia require urgent investigation because of the risk of hyponatraemia associated with congenital adrenal hyperplasia (CAH) and to permit an informed decision on gender assignment. CAH is the commonest form of DSD, accounting for around 80% of all infants born with ambiguous genitalia. Despite controversy regarding timing and consent, feminizing genitoplasty in early childhood remains the accepted management for girls with significant clitoromegaly. Surgical reconstruction for 46XY DSD is guided by several factors, notably the size of the phallus and gonadal phenotype. The majority of individuals with disorders of sex development will require ongoing specialist care and long-term multidisciplinary follow-up and support.