The Hungarian Centre for Congenital Anomaly Control manages a number of surveillance programmes based on the Hungarian Congenital Malformation Registry. Notification of congenital anomalies, which is compulsory, originates exclusively from physicians working in various health institutions and is based on their diagnosis of malformed patients--newborns and infants. In recent years, the total birth prevalence of registered congenital anomalies has exceeded 47 per 1,000 total births. The notified data are critically evaluated and centrally coded according to the unit of notification, the affected individual. Diagnostic accuracy, completeness of notifications and the effect of confounding variables are continuously checked. The purpose of the Case-Control Surveillance System is to obtain etiological information concerning drug consumption, maternal diseases and occupational hazards during pregnancy. The surveillance of mutations through indicator conditions (sentinel anomalies. Down's syndrome and pairs of components of unidentified multiple congenital anomalies) is an attempt to measure the rate and trend of new germinal mutations. The nationwide follow-up of multimalformed infants helps to increase the proportion of identified congenital anomaly entities, to identify new ones, and to detect clusters caused by new environmental teratogenic or mutagenic factors.