Aim: The objective of this retrospective cohort study was to evaluate whether evidence from randomized clinical trials on the successful treatment of intrabony defects by regenerative therapy can be transferred to patients in a private periodontal practice. Material and Methods: In 191 patients a total of 1099 teeth with intrabony defects were treated using bovine bone mineral with or without collagen membrane. Defects were classified as 1- and 2-wall and as shallow (11 mm). A total of 1008 defects in 176 patients were monitored clinically and radiographically for collection of 1-year short-term, mid-term (2-4yrs) and long-term (5-10yrs) data. Baseline measurements were taken clinically and radiographically for standardisation of defect size. IMAGE J Software allows measurement accuracy of 0.01 mm. During supportive periodontal therapy, measurements were recorded from 1y post-operative x-rays (N=1008) and at following investigation stages, up to 10 years (mean 5.2 years). Change in radiographic bone levels was used as primary outcome parameter. Due to lack of compliance or supportive care alio loco, 15 patients (91 teeth) were excluded from analysis. Results: Overall a mean radiographic bone fill of >50% was observed. Deep and moderate defects showed a higher degree of radiographic bone fill than shallow defects (54,5% vs. 50% vs. 43,3%). Radiographic bone gain obtained at 1year remained stable during mid-term and long-term follow-up. Tooth loss amounted to 2.6% and was dependent on initial defect size (1.2% for shallow, 1.4% for moderate, 5.7% for deep defects) and occurred mainly due to endodontic failures. Conclusion: Under conditions of daily periodontal practice, regenerative treatment using bovine bone mineral with or without collagen membrane can lead to a mean defect resolution of greater than 50%, based on radiographic (2D) measurement. A 3D defect reconstruction of approximately 75% can be assumed from this finding. The radiographic bone gain achieved at 1y post-operatively could be maintained up to 10 years after surgical intervention in patients with compliance to periodontal supportive care. Keywords: periodontal regenerative surgery, long-term attachment level gain, DBBM