In foetuses at risk of virilising CAH, prenatal treatment can be offered by administration of dexamethasone (DEX) via the mother in order to prevent genital malformations. Accumulating evidence from animal studies and epidemiological data raise concerns regarding the long term consequences of excess glucocorticoids on the developing foetus. The European study PREDEX is organized as an open, controlled, non-randomised, multicentre trial. The impact of DEX on the general well-being of the mother is studied as well as the glucose homeostasis, bone metabolism, and cardiac- and lipid profile. Fetal growth is followed and the treated children are followed until 18 yrs of age regarding potential DEX effects on blood pressure, renal function, bone mineralisation, glucose tolerance, lipid profile, function of the hypothalamicpituitaryadrenal axis, motor skills and brain morphology. In addition, psychosocial development and cognitive development in treated children is evaluated. Until now 26 cases has been enrolled in the PREDEX study. A second, retrospective follow-up study regarding neuropsychological and behavioural development of DEX treated cases has been accomplished. Of 40 DEX treated children, 26 (median age 11 yrs) participated in the study. Thirty-five sex- and age matched healthy children were controls. No between-group differences could be observed concerning psychometric intelligence, measures of cerebral lateralization, memory encoding, long term memory, psychopathology, behavioural problems and adaptive functioning. However, short term treated, CAH unaffected children performed worse than the control group on a test assessing verbal working memory (P=0.003), and on self-perception of scholastic competence (P=0.003). This group also showed increased self-rated social anxiety (P=0.026) and in a questionnaire on temperamental traits the children were described by their parents as being more sociable than controls (P=0.045). These findings may thus question future DEX treatment of CAH.