OBJECTIVE: The purpose of the present study was to describe the severity and pattern of peri-implantitis-associated bone loss. MATERIAL AND METHODS: Intra-oral radiographs from 182 subjects were analysed. Bone-level measurements were performed in 419 implants with a history of bone loss. All radiographs obtained in the interval from the 1-year follow-up to the end-point examination (5-23 years) were analysed. The amount of bone loss that occurred from 1 year after prosthesis insertion was assessed and the pattern of bone loss was evaluated. RESULTS: The average bone loss after the first year of function was 1.68 mm and 32% of the implants demonstrated bone loss > or =2 mm. The multilevel model revealed that the bone loss showed a non-linear pattern and that the rate of bone loss increased over time. The model also revealed that the pattern of peri-implantitis associated bone loss was similar within the same subject. CONCLUSION: It is suggested that peri-implantitis-associated bone loss varies between subjects and is, in most cases, characterized by a non-linear progression, with the rate of loss increasing over time.