Eighty-one 35-year-old Oslo citizens examined in 1973 were reexamined after 15 years, to monitor changes in their caries situation expressed as carious surfaces (DS + DFS). Factors considered to be of importance for a change in the number of carious surfaces over this 15-year period were arranged under four items: environment, behavior, human biology, and health care organization. The results showed a slight but not statistically significant increase in the overall caries experience expressed as DMFS. A statistically significant reduction in DS + DFS from the age of 35 to 50 years was demonstrated. Despite this reduction 23% of the 50-year-olds had more carious surfaces than at age 35. The results indicate that the improvement in the number of untreated carious surfaces reported from many Western societies is also valid for adult Norwegians. However, this improvement is not shared by all. Multivariate analyses showed that behavioral factors had the greatest impact on the observed changes in dental health.