Background: Periodontal research has focused on clinical outcomes of periodontitis and in a lesser extent on patient-reported outcomes. Objective: The objectives of this study were to 1) determine oral health-related quality of life (OHRQoL) before the first step and after the second step of periodontitis therapy and 2) compare sociodemographic and clinical characteristics with changes in OHRQoL. Methods: Patients with periodontitis that had never been treated with subgingival plaque instrumentation were recruited. Clinical parameters were recorded. A questionnaire was applied to collect sociodemographic data, smoking status, and pain. The Oral Health Impact Profile-14 (OHIP-14) was used to evaluate OHRQoL before the first step and after the second step of periodontitis therapy. Results: Fifty-one participants completed the study, mean age 46.88 years ± 11.16. OHIP-14 total score decreased from 16.98 ± 11.48 to 8.41 ± 9.06 after treatment. Improvements in physical pain, psychological discomfort, physical disability, psychological disability, social disability, and handicap accounted for the changes. The most frequent periodontal staging was stage III. As for grading, Grade A was diagnosed in 16 (31.37 %) participants, Grade B in 16 (31.37 %), and Grade C in 17 (33.33 %). Mean plaque index was 61.4 % ± 17.6 before the first step of periodontitis therapy and 22.8 % ± 10.6 after. Pain in the last month decreased after periodontal care. No differences in OHRQoL changes were detected when comparing age categories, gender, and educational level. Better scores were reported from non-smokers, before and after therapy (p = 0.003). Conclusion: Periodontal therapy had a positive impact on self-perceived quality of life of patients.