Multi-factorial risk models have been proposed to enhance the ability to predict risk for the progression of treated chronic periodontitis. to study if the outcomes of supportive periodontal therapy (SPT) based on a multi-factorial periodontal risk assessment are influenced by IL-1 gene polymorphism (IP) status. Information about the IP and smoking status, clinical periodontal conditions and age related bone level measurements were used to calculate a peridontal risk assessment model (PRA). The surface area of this diagram was calculated for 224 subjects who had participated in an SPT program over four years. Baseline and 4-year follow-up data were studied in relation to the IP status. Positive IP tests were obtained for 80/224 (35.7%) of the subjects. At baseline the mean PRA for the IP positive group was 79.9 units, which at year four had increased to 81.3 units (mean diff: 1.4 units, S.D. 16.5, p0.45, 95% CI: 2.3 to 5.1). At baseline and year four the mean PRA for the IP negative group was 44.2 and 38.6 units, respectively. This difference was statistically significant (mean diff: 5.6, S.D. 16.1, p0.001, 95% CI: 3.0 to 8.3). Independent t-tests confirmed that the IP status was significantly associated with a less favorable change in PRA over the four-year period (PRA difference: 7.04, t=3.01, p0.003, 95% CI: 2.4 to 11.65). Bleeding on probing, and probing depth values alone did not differ between positive and negative IP status. Regression analysis demonstrated that the best-fit model for change in PRA included bleeding on probing at baseline, IP status, proportional alveolar bone loss in relation to the age, and gender. The PRA allowed the assessment of the outcomes of SPT therapy. Subjects with positive IP did not respond to individualized SPT as favorably as did IP negative subjects. Keywords: periodontal risk assessment, bleeding on probing, alveolar bone height, multi-functional risk model, interleukin-1 polymorphism, supportive periodontal therapy