The purpose of the present study was to investigate time trends in primary reasons for extraction of permanent teeth in Norway from 1968 to 1988. Johansen studied reasons for extraction of 8757 teeth in 4216 patients during a 3-week period in 1968. Twenty years later a random sample of 500 Norwegian dentists provided particulars about all extractions carried out during a 2-week period. 350 dentists (70%) replied in 1988 but 96 of them had not extracted any teeth during the observation period. Reasons for extraction of 985 teeth from 692 patients were available for analysis. Caries and its sequelae accounted for 35%, periodontitis for 19%, and orthodontic reasons for 20% of extractions in 1988. A comparison of the distribution of extraction according to reasons for patients over 20 yr of age revealed a highly significant difference between 1968 and 1988 (P less than 0.001) mainly due to a decrease in the role of caries and an increase in extractions for other reasons. Caries and its sequelae accounted for a higher proportion of extractions than periodontitis at all ages over 20 yr in 1968, only up to 45 yr of age in 1988. Thus it is concluded that the observed time trend in primary reasons for extraction corroborates expectations based on declining caries prevalence, increasing retention of teeth and a rise in dental attendance in Norway during the last 20 yr.