What are the respective places for prenatal treatment and neonatal screening in 21 hydroxylase deficiency, (21OHD) CAH? Current diagnostic procedures for 21OHD CAH do not prevent potential or actual morbidity and mortality from salt wasting and hypoglycaemia, ambiguous genitalia and late diagnosis. Presentation is with life-threatening illness or virilisation with long-term physical, psychological and psychosexual sequelae. Screening the whole newborn population would add only a very small additional unit cost in the screening laboratory already measuring TSH and phenylalanine. There are still few data on which to base an assessment of the efficacy of neonatal screening in reducing morbidity and mortality. Screening should now be adopted on a regional, or national, basis to assess both efficacy and cost-effectiveness. Although more (uncontrolled) data are now available concerning prenatal dexamethasone therapy, the degree of benefit in terms of reduced virilisation in relation to potentially significant maternal side effects is unclear and possible long term childhood side effects have not been studied. At present, therefore, there is insufficient evidence regarding the safety of mother and fetus to recommend the general use of dexamethasone outwith the context of controlled scientific studies. There is an urgent need for prospective controlled studies to be undertaken which would, in time, resolve both questions.