The purpose of this study was to investigate the clinical effects of erbium, chromium: yttrium, scandium, gallium, garnet (Er, Cr: YSGG) laser treatment as a complementary to scaling and root planning (SRP) during the treatment of chronic periodontitis and gingival crevicular fluid (GCF) interleukin-1 beta (IL-1β), interleukin-6 (IL-6), and interleukin-35 (IL-35) levels. Forty patients with chronic periodontitis were divided into two equal groups at random to receive SRP alone and SRP followed by Er, Cr: YSGG laser treatment, which are control and test groups, respectively. Clinical attachment level (CAL), probing depth (PD), bleeding on probing (BOP), gingival index (GI), and plaque index (PI) were measured for all patients in both groups at baseline and again at the end of the 1st, 3rd, and 6th months following the treatment. Levels of GCF IL-1β, IL-6, and IL-35 were analyzed by enzyme-linked immunosorbent assay. After periodontal treatment, CAL, PD, BOP, GI, and PI, which are clinical parameters analyzed, decreased significantly (P < 0.05) in both test and control groups. GCF volume, IL-1 β, IL-6, and IL-35, levels in both groups proved statistically significant reductions compared to the baseline (P < 0.05), but no substantial variations were detected among both groups. According to these results, we can suggest that IL-35 may be related to the pathogenesis of periodontitis and that Er, Cr: YSGG laser can be used as an adjunct to SRP in periodontal treatment.