This contribution describes and compares the causes of hearing disability in a cohort of children, born 1980-90, provided with hearing aids and included into the longitudinal surveillance programs of hearing-disabled children performed in two pediatric audiological units within the Copenhagen area. In addition the causes of hearing disability in childhood are compared with the causes found in a cohort born 1970-80, within the same geographical area, using the same criteria for hearing disability and diagnostic classification. No significant differences in the etiology of hearing disability were present in the two districts, and in the combined area prenatal causes accounted for 55% with inheritance (46%) being the most prominent cause of hearing disability. A significant increase in the incidence of inherited hearing disability among the prenatal causes from 69% in the 1970-80 cohort to 85% in the 1980-90 cohort was demonstrated, while a significant decrease in the incidence of foetal infection (i.e. rubella) from 27% to 9% within the two decades was demonstrated. No significant changes in the perinatal and postnatal causes were found from the 1970-80 to 1980-90 cohort, and although an improvement in the' diagnostic procedures was found - i.e. a reduction from 26% to 20% in the incidence of unknown cause - the difference in the incidence of unknown cause is insignificant between the two decades. The investigation supports the need for continuous monitoring of the causes of hearing disability in childhood and supports the potential value of worldwide accepted criteria for etiological categories.
