The aim of this retrospective study was to evaluate the influence of interleukin (IL)-1 genotype on the clinical parameters pocket probing depth and tooth loss in periodontally treated and regularly maintained patients. Only data from non-smokers were included. Patient mean data on pocket probing depth (PPD) and tooth loss from 53 Caucasian patients treated for generalized chronic periodontitis and maintained for an average of 15.5 years at the university of Kiel were analysed. All patients were genotyped and subjects with at least one copy of the variant allele 2 at positions IL-1A -889 and IL-1B +3954 were classified IL-1 genotype positive. 12 patients (22.6%) were IL-1 genotype positive. IL-1 genotype positive/negative patients were on average 46.3/45.8 years old with a mean of 23.8/23.9 teeth, resp., at baseline (TO). A total of 86 teeth were lost initially, resulting in an average of 21.5/ 22.5 teeth after active treatment (T1). The corresponding values after 13 years of supportive periodontal care (T2) were 20.7/21.6 teeth. Corresponding mean PPD values for IL-1 genotype positive/negative patients decreased from 4.7 mm/5.3 mm (To) to 2.9 mm/ 2.9 mm (T1) and increased slightly to 3.3 mm/3.4 mm at T2. Intergroup differences of PPD and tooth loss were not significant. Regarding pocket probing depth and tooth loss, there were no significant differences related to IL-1 genotype.