Objectives: Presence of clinical attachment loss on the distal aspect to the second molar may be associated with malposition of the third molar. The aim of this study was to evaluate the reduction of clinical attachment loss at the distal aspect of the second molar after third molar extraction and application of leukocyte- and platelet-rich fibrin (L-PRF). Method and materials: Eighteen subjects with a clinical attachment loss on the distal site to the second molar associated with impacted third molar in both sides of the jaw were recruited for the study. For each subject the teeth were randomly allocated in test and control groups. After surgical removal of the impacted third molar, the L-PRF was inserted in the fresh alveolar socket of test sites; in the control sites no graft was inserted after extraction. Full-mouth plaque score, full-mouth bleeding score, clinical attachment level (CAL), probing depth, and gingival recession were assessed at baseline and 6 months later. Results: After 6 months, mean CAL change was 1.99 ± 1.18 mm in the test group and 1.15 ± 1.01 mm in the control group; probing depth change was 1.33 ± 0.87 mm in the test group and 0.50 ± 0.63 mm in the control group. Statistically significant differences (P .05) were observed between groups in terms of CAL and probing depth changes. No differences were found in gingival recession changes. Conclusion: Within the limits of the present study, the sites treated by means of application of L-PRF after impacted third molar extraction showed better results in terms of CAL gain and probing depth reduction when compared with control sites. Keywords: clinical attachment level, periodontal defects, platelet-rich fibrin, third molar