The reasons for extraction of teeth were determined in a Canadian population sample of 909 patients, ranging in age from 14 to 91 years. Caries was the primary cause of extraction (63%), followed by periodontitis (34%). For the adult age groups, the percentages were approximately the same. While periodontitis was the cause of one-third of the extractions, these occurred in only one-fifth of the population. Although there is a commonly expressed belief that periodontitis is the major cause of tooth loss in adults, a review of both historical and contemporary literature does not support this position. According to the current concept of the natural history of periodontal disease, only about one-fifth of the population, or less, is likely to have periodontitis severe enough to cause tooth loss. This view is consistent with data from this and most other studies on the reasons for tooth extraction.