Aims: To evaluate whether the alveolar osteitis (AO) incidence after extracting partially erupted third molars differs when platelet-rich fibrin (PRF) is administered in the alveolar socket and to assess the influence of PRF on postoperative pain levels and periodontal probing depth. Settings and Design: In this split-mouth randomized study, 50 patients (17 men/ 33 women; mean age, 23.96 years) with bilateral symmetric partially erupted mandibular third molars were enrolled. Material and Methods: PRF was randomly placed in one extraction socket, whereas the other socket was left empty. A verbal rating scale was used to evaluate postoperative pain levels. AO development was evaluated on the 7th postoperative day. At 3 months postoperatively, periodontal probing depth was measured on the distal surface of the second molars. Results: In total, 8% of patients in the PRF group and 18% of the patients in the control group were diagnosed with AO. None of the smokers in the PRF group and 37.5% smokers in the control group were diagnosed with AO. Mean postoperative pain levels were lower in the PRF group than in the control group at all time points. At 3 months postoperatively, periodontal probing depths were found to be %3 mm in both groups. Conclusions: PRF significantly reduced the AO incidence among smokers and had a positive effect on postoperative pain levels but not on periodontal healing.