Within the framework of a retrospective epidemiological investigation concerning the incidence of CNS-malformations in the city of Cologne during the period 1971-80, 76 749 hospital births assessed from records in six hospitals were considered. This represents 88% of all hospital births. The incidence varied between 0.79-1.80 with a mean of 1.37/1000 total births. This figure was primarily influenced by the values obtained from Spina bifida (0,59/1000). If the dates for the period 1961-70 are included, a marginal increment is exhibited (from 1.13 up to 1.37/1000) for the total occurrence of CNS-births, as opposed to a slight decrease for the Sb-group (0,65 down to 0.59/1000). A seasonal variation was not revealed for the total number of births. Contrary to worldwide literature, the male rates were significantly higher (113 : 100). The stillbirth-rate was 23,8% compared to 0,63% of total births, whereby hydrocephalus cases with 52% were heavily represented. A relationship between mother's age and incidence of occurrence was, as in the previous decade, not substantiated. Since the dates presented are obtained on the basis of hospital obstetrics records, it is unlikely that similar figures will arise in future studies, due to improved prenatal diagnosis (sonography and amniocentesis), which influence decisions relating to the possibilities of interruption of pregnancy.