Although there has been a wide range of reports on the average number of teeth and the average dental expenses of elderly people in each municipality in Japan, no report describing the relation between the average number of teeth and the average dental expenses was found. On the basis of previous studies, we proposed a hypothesis that the average dental expenses of elderly people is high in the municipalities where the average number of teeth in elderly people was high, due to the high rate of dental treatment in elderly people and we performed an ecological study in order to check this hypothesis. Stepwise regression analysis was performed using a criterion variable : the average dental expenses of the elderly people insured by national health insurance in May 1999, and explanatory variables : the average number of teeth in elderly people, the number of dentists in clinics or hospitals per a population of 100, 000, the population density, the ratio of aging population, the ratio of employees engaged in primary industry, the ratio of employees engaged in tertiary industry and the average amount of a residents' tax, and a weighting variable : the number of the elderly people insured by national health insurance, for each of the 62 municipalities in Shizuoka prefecture. The result was as follows. Population density and the average number of teeth in elderly people were selected for analysis. Because the average number of teeth in elderly people was statistically significant (p<0.01) in analysis when the other variables describing characteristics of a municipality were controlled, it was found that the average dental expenses of elderly people was high in the municipalities where the average number of teeth in elderly people was high. After that, a path analysis was performed on the basis of the model that the average dental expenses of elderly people is influenced by the rate of dental treatment, the average number of days of dental care per patient, and the average dental expenses per elderly patient per day in each municipality. The rate of dental treatment, the average number of days of dental care per patient and the average dental expenses per elderly patient per day is each influenced by population density and the average number of teeth in elderly people for each municipality. The result was as follows. The relation between the rate of dental treatment and the average dental expenses, and the relation between the average number of teeth and the rate of dental treatment was shown. Subsequently, it was found that the average rate of dental treatment was high in the municipalities where the average number of teeth was high, and that the average dental expenses of elderly people was high in the municipalities where the average rate of dental treatment was high. We were able to successfully confirm our hypothesis.