OBJECTIVE: To investigate outcomes of ultrasound investigations (US) and invasive diagnostic procedures in cases of congenital malformations (CM), and to compare the use of invasive prenatal test techniques (amniocentesis (AC) versus chorionic villus sampling (CVS)) among European populations. DESIGN: Analysis of data from population-based registries of CM. SUBJECTS: 25 400 cases of CM recorded by 14 EUROCAT registries covering a total population of 1,013,352 births 1995-99. RESULTS: US were performed in 91% of cases, and positively detected CM in 35% of cases. AC was performed in 24% of the cases and CVS in 3% of cases. Thirty-eight percent of invasive tests gave positive results. Fifty-two percent of cases with maternal age > or = 35 years had an invasive test performed compared to 20% of cases with younger mothers.Considerable variation was found between registries in the uptake rate of invasive tests in cases with older maternal age and on the use of invasive tests with only four regions employing CVS techniques in at least a third of the cases having invasive tests. For chromosomal anomalies US gave positive results in 46% of cases with maternal age < 35 years with US performed and in 36% of cases with maternal age > or = 35 years with US performed. CONCLUSION: Prenatal US was performed in 91% of all pregnancies with CM but the test was only positive in a third of the cases. There was large regional variation in the uptake rate of invasive tests with maternal age of 35 years or more. For every CVS carried out there were nine AC tests. US is an important tool in the prenatal diagnosis of chromosomal anomalies in Europe.