Introduction/Objective The objective of the study was to investigate whether there are differences in therapeutic effect between initial treatments of chronic periodontitis [scaling and root planning (SRP)] alone and SRP in conjunction with injectable platelet-rich fibrin (I-PRF) application, comparing clinical parameters after three months. Methods Twenty-four patients with chronic periodontitis who had at least two sites with probing pocket depth (PPD) ≥ 5 mm on contralateral side participated in the study. Using a split-mouth design, the patients were treated with SRP + I-PRF (study group) or SRP only (control group). The clinical parameters, clinical attachment level (CAL), gingival margin level (GML), PPD, bleeding on probing, and plaque index, were recorded on both sides. Results Compared to baseline, both treatment modalities demonstrated an improvement in investigated clinical parameters. The mean value of CAL was reduced from 1.97 ± 0.75 (0.25-3.31) to 1.07 ± 0.44 (0.12-1.78) in the study group, whereas it decreased from 1.81 ± 0.66 (0.42-2.96) to 1.48 ± 0.55 (0.22-2.30) in the control group. Similarly, the corresponding values for GML and PPD showed statistically significant difference between the groups (p = 0.040 and p = 0.006, respectively). Conclusion Regardless the limited number of patients in the study, initial periodontal therapy in conjunction with injectable platelet-rich fibrin proved to display significant improvement in all clinical parameters compared to initial periodontal therapy alone.