Background: Lack of consensus on the clinical parameters of peri-implantitis may complicate accurate diagnosis of the disorder. Furthermore, the lack of reliable estimates of the diagnostic capacity of the clinical endpoints precludes the definition of an effective treatment protocol for periimplantitis. The present canine study assesses the diagnostic accuracy of the clinical parameters for monitoring the peri-implant tissues in a controlled ligature-induced peri-implantitis model followed by a spontaneous progression phase. Material and methods: Six beagle dogs were followed-up on during three episodes of ligatureinduced peri-implantitis and a further episode of spontaneous progression. Probing depth (PD), bleeding on probing (BOP), mucosal recession (MR) and suppuration (SUP) were recorded at four sites per implant and at four study timepoints. Moreover, the implant mucosal index (IMI) was calculated at implant level. Marginal bone loss (MBL) was determined using computed tomography at four sites per implant. A linear regression model was used to estimate clinical and radiological parameters during peri-implantitis progression. Results: Progressive peri-implant bone loss is characterized by an increase in PD, more profuse BOP, MR and SUP in advanced cases (p<0.001). However, even in the presence of severe bone loss, SUP was not a common finding, with an incidence of approximately 10% at the last timepoint. These clinical parameters were significantly correlated to MBL at most of the timepoints. The implant mucosal index in turn showed a positive correlation to MBL and the peri-implant inflammatory signs (r=0.39; p<0.001), with a tendency to exhibit higher scores in the course of ligature-induced periimplantitis, followed by a slight decrease during the spontaneous progression period. Conclusion: The clinical features of peri-implantitis and spontaneous progression of the disorder may facilitate an accurate diagnosis of peri-implant pathogenic bone loss.