The incidence of congenital malformations reported to the Register of Births during 1976-77 in various socioeconomic groups were studied combining the informations from the birth register with that from the 1975 census (including occupation of the mother, income of the family, type of family and housing standard). The total population of 190 024 infants were divided into three groups; 6915 infants (3.6%) were assigned to the most privileged group (group I) and 26 430 (13.9%) to the less privileged group (group III). The total incidence of 5.01% of any malformation did not differ significantly between the groups. Neither was any variation found for specific malformation types, such as neural tube defects, cleft palate or morbus Down.