Objectives: Assessment of patient-related factors contributing 1) to tooth loss and 2) to the quality of treatment outcome 10 years after initiation of anti-infective therapy. Methods: All patients who had received active periodontal treatment 10 years ago by the same examiner were recruited consecutively until a total of 100 patients was re-examined. Re-examination was performed by a second examiner and included: clinical examination, test for interleukin-1 polymorphism (IL-1), smoking history, review of patients' files (i.e. regularity of supportive periodontal therapy: SPT). Statistical analysis included Poisson and logistic regressions. Results: Fifty-three patients attended SPT regularly, 59 were females, 38 were IL-1 positive. Poisson regressions identified mean plaque index during SPT, irregular attendance of SPT, gender (p = 0.0001), initial diagnosis (p = 0.0005), IL-1 polymorphism (p = 0.0007), smoking (p = 0.0053), and age (p = 0.0487) as factors significantly contributing to tooth loss. Additionally mean plaque index during SPT (p = 0.011) and irregular SPT (p = 0.002) were associated with a worse periodontal status 10 years after initiation of therapy. Conclusion: The following risk factors for tooth loss were identified: ineffective oral hygiene, irregular SPT, IL-1 polymorphism, initial diagnosis, smoking, age, and gender. Keywords: long-term results, periodontal therapy, prognosis