The purpose of this split-mouth, single-blind, controlled clinical study was to evaluate the impact of low-level laser therapy (LLLT) as an adjunct to non-surgical treatment of chronic periodontitis. Twenty-five systemically healthy and non-smoking adults with chronic periodontitis who had at least two bilateral premolar teeth with probing pocket depth (PPD) of 7 aeyenaEuroex aeyenaEuroe5 mm were included in the study. In the periodontal examination of these patients, PPD, gingival index (GI), plaque index (PI), clinical attachment level (CAL), and bleeding on probing (BOP) were recorded at the baseline, first, third, and sixth months after treatment. Gingival crevicular fluid (GCF) samples were taken at the baseline, first week, and first month after treatment. The collected GCF samples were analyzed using the MAGPIX (TM) system with a Bio-Plex Pro (TM) Human Cytokine 27-plex kit. After non-surgical periodontal treatment, LLLT with an energy density of 7.64 J/cm(2) was performed four times: immediately after scaling and root planning (SRP) and on the first, third, and seventh day after treatment. In the first month, PPD levels were significantly (p < 0.05) lower in the SRP + LLLT group than in the SRP group. At the third and sixth months, CAL, PPD, and GI were significantly (p < 0.05) lower in the SRP + LLLT group than in the SRP group. Differences in GCF cytokines levels among the group were not statistically significant. Within the limitations of this study, it is indicated that LLLT as an adjunct to non-surgical periodontal treatment has a positive impact on clinical parameters.