Purpose: We aimed to investigate the impact of nonsurgical periodontal treatment combined with one-year dietary supplementation with omega (${omega}$)-3 on the serum levels of eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), docosapentaenoic acid (DPA), and arachidonic acid (AA). Methods: Fifteen patients with chronic generalized periodontitis were treated with scaling and root planing. The test group consisted of seven patients ($43.1{pm}6.0$ years) supplemented with ${omega}$-3, consisting of EPA plus DHA, three capsules, each of 300 mg of ${omega}$-3 (180-mg EPA/120-mg DHA), for 12 months. The control group was composed of eight patients ($46.1{pm}11.6$ years) that took a placebo capsule for 12 months. The periodontal examination and the serum levels of DPA, EPA, DHA, and AA were performed at baseline (T0), and 4 (T1), and 12 (T2) months after therapy. Results: In the test group, AA and DPA levels had been reduced significantly at T1 (P<0.05). AA and EPA levels had been increased significantly at T2 (P<0.05). The ${Delta}EPA$ was significantly higher in the test compared to the placebo group at T2-T0 (P=0.02). The AA/EPA had decreased significantly at T1 and T2 relative to baseline (P<0.05). Conclusions: Nonsurgical periodontal treatment combined with ${omega}$-3 supplementation significantly increased the EPA levels and decreased the AA/EPA ratio in serum after one year follow-up. However, no effect on the clinical outcome of periodontal therapy was observed.