Purpose: The aim of this study was to assess the accuracy of linear measurements of bone loss within infrabony defects on digitized radiographs after digital filtering particularly designed to image periodontal bone loss. Methods: Before surgery 50 standardized radiographs of 50 infrabony defects were obtained. Intrasurgically the distances from the ce-mentoenamel-junction (CEJ) to the alveolar crest (AC), from the CEJ to the bottom of the bony defect (BD), and the depth of the infrabony component (INFRA) were assessed. All radiographs were digitized and the distances CEJ-AC, CEJ-BD, and INFRA were measured on digitized but unchanged radiographs and after use of the filter. Results: There was a small overestimation of CEJ-AC (0.35-0.68 mm) and underestimation of CEJ-BD (0.84-1.12 mm) and INFRA (0.66-0.76 mm). Accuracy of measurement of the distance CEJ-AC was influenced by vertical angulation difference (p = 0.047) and the intrasurgical CEJ-AC (p = 0.003). Accuracy of CEJ-BD was influenced by intrasurgically assessed bone loss (p = 0.012). Accuracy of INFRA was influ-enced by individual patient, intrasurgically assessed INFRA (p Keywords: periodontal bone loss, infrabony defects/diagnostics, radiography, dental, radiography, dental, linear measurements, angle measurements