BACKGROUND The aim of this study was to determine the current prevalence and quality of endodontic treatments and investigate the relationship of various factors with posttreatment endodontic disease (PTED) in a Turkish subpopulation. MATERIAL AND METHODS The cone beam computed tomography (CBCT) images of 1069 patients (male, 50.9%; female, 49.1%; mean age, 45.32±13.50 years) were retrospectively analyzed. A total of 20 646 teeth were examined; 1604 had undergone root canal. Periapical status was assessed using a modified CBCT periapical index. The relationship between periapical status and quality of root canal fillings (RCFs) was analyzed statistically using the chi-square test. Multivariate logistic regression was performed to evaluate the effect of individual parameters by adjusting them for other variables. RESULTS A total of 7.8% of all teeth had RCF. The prevalence of poor filling (having at least 1 procedural error) was 54.1%; the prevalence of PTED was 56.8%. The prevalence of PTED was 44.3% in teeth with short RCF, 10.8% with overextended RCF, 35.7% with nonhomogeneous RCF, and 15.5% in teeth with untreated root canals. The rate of RCF teeth with procedural errors associated with PTED was 76.2%. There was no significant difference between sexes in apical periodontitis (P>0.05), which developed more frequently in teeth with procedural errors. CONCLUSIONS The overall prevalence of poor fillings (having at least 1 procedural error) among RCF teeth was high (54.1%) in this subpopulation. There is a substantial need to improve the technical quality of endodontic treatment.