A baby born with ambiguous genitalia always causes immense distress and concern. It has to be emphasised that handling of this situation needs to be performed by senior staff with experience as major mistakes can occur in the diagnosis and interpretation of results and in the correct assignment of sex. The presence of one or two palpable gonads may help with the interpretation of subsequent results. Chromosomal karyotype is valuable but the genotype is not necessary a good guide to the decision about the sex of rearing. On account of major changes in the adrenal gland in the first three days of life, it is not helpful to collect a plasma or urine sample until after 72 hours of post natal age. Gestational age needs to be taken in to consideration when interpreting the 17 hydroxy progesterone levels as they are much higher in preterm infants. Under virilisation of a male is of greater severity than virilisation of a female infant as it is usually more difficult to achieve satisfactory outcome.