OBJECTIVE: To evaluate the outcome of initial periodontal therapy and additional diode laser decontamination therapy on clinical parameters and the amount of tumor necrosis factor alpha (TNFα) in gingival crevicular fluid (GCF) in patients with chronic periodontitis. STUDY DESIGN: The study included 22 patients who were diagnosed with chronic periodontitis and who had at least 1 (≥5 mm) periodontal pocket in the posterior region of each upper left hemiarcade. The study was designed as a splitmouth study involving mechanical therapy on the right side and nonsurgical periodontal therapy plus diode laser decontamination therapy on the left side. RESULTS: A statistically significant decrease was observed in clinical parameters at 3 months when compared to the values at baseline in both treatment areas. The change in clinical parameters at 3 months after therapy was not significantly different between the groups (p>0.05). The comparison of GCF TNFα levels at baseline and at 3 months in the 2 treatment areas identified significant changes in the TNFα levels in the hemiarcade treated with laser diode contamination therapy, whereas the changes in the hemiarcade treated with nonsurgical periodontal therapy were not significant (p>0.05). A betweengroup comparison revealed no statistically significant difference at 3 months posttherapy, while the difference at 1 month was found to be statistically significant. CONCLUSION: The study found that laser therapy in addition to nonsurgical periodontal therapy has a positive effect on the clinical parameters and proinflammatory TNFα levels in the early period but makes no contribution in the long term. © 2020 Science Printers and Publishers Inc.. All rights reserved.