The purpose of this study was to quantify treatment outcomes of endodontically treated teeth, in a representative, population-based adult sample. The "Florida Dental Care Study" was a prospective, longitudinal, cohort study of 873 subjects who had at least one tooth at baseline and who were 45 yr or older. An in-person interview and clinical examination were conducted at baseline, 24 months, and 48 months after baseline, with 6-monthly telephone interviews between those times. Dental record information was abstracted afterward. Seventy-five teeth had conventional root-canal therapy (RCT) performed and met the inclusion criteria of 1-yr of follow-up or extraction. The mean duration of follow-up after RCT was 24.8 months. The mean (SD) attachment loss (AL) on teeth receiving RCT was only 3.3 (1.4) mm. Permanent restorations were placed in 79% of teeth a mean of 4.4 months after the RCT. However, 12% of teeth did not have any restorative treatment after RCT. After RCT had been completed, 81% of teeth were retained and 19% were ultimately extracted. Taken as a whole, this community-based study of a representative sample of adults suggests a higher failure rate than reported from studies in highly controlled environments or insured populations. It also suggests that the length of time to initial restoration of RCT-treated teeth is less than optimal. RCT was almost never performed on teeth with advanced periodontal attachment loss.