Eight children excessively exposed to benzodiazepines (BZD) in utero are described. Five of the 8 mothers admitted regular use of BZD and in 3 mothers, stored serum from early pregnancy could be analysed and found positive for BZD and its metabolite. All the children had similar dysmorphic features, in addition, 1 child had aplasia of one kidney and 2 had cleft palate. At follow-up 2 children had become microcephalic. 2 were severely mentally retarded, 5 had a mild mental retardation and only 1 was of normal intelligence. In a case-control study, 4 neonatal diagnoses of congenital malformations, in our experience characteristic of fetal BZD exposure, were chosen as inclusion criteria. In 8 of 18 cases, blood samples from early pregnancy were positive for BZD as compared to 2 of 60 control samples. An association between BZD-positive serum tests and the particular diagnoses could be demonstrated (p = 0.00006).