Background: due to limitations of scaling and root planning in certain cases of periodontal disease, the adjunctive use of antimicrobials, systemically or locally, has been indicated in order to improve the clinical outcomes of these conditions. Aim: to evaluate the efficiency of metronidazole dental gel associated to scaling and root planning in the improvement of periodontal parameters. Material and methods: a split mouth randomized clinical study was conducted in 40 patients with chronic periodontitis receiving scaling and root planning alone, metronidazole dental gel alone and scaling and root planning associated with metronidazole dental gel. Clinical examinations were performed at baseline, 1 month and 3 months. Results: scaling and root planning combined with metronidazole gel showed short term advantages in improving the clinical parameters, the best results being noted at 3 months. Conclusion: subjects with chronic periodontitis have significant benefits from scaling and root planning when used with metronidazole dental gel as an adjunct.