Statement of Problem: Intraoral radiographs are the most common diagnostic tool used to assess alveolar bone loss with periodontal origin. However, radiographic assessment tends to underestimate the amount of bone loss. Digital processing and manipulation of radiographic images may enhance diagnostic interpretation of radiographs.Purpose: The aim of the present study was to evaluate the validity of linear measurement of intraosseous periodontal lesions by conventional periapical (PA) and digitized radiographs in comparison with clinical measurements.Materials and Methods: In this practical study, 35 standard conventional PA radiographs (Parallel technique) were obtained from 50 vertical periodontal osseous lesions. During mucoperiosteal full thickness flap surgery, the distances between the depth of periodontal osseous lesions and the crest of interproxiaml bones were measured and compared with liner measurements of the lesions by conventional PA radiographs and digitized radiographs manipulated by gamma adjustment Photoshop 7.0 software for statistical evaluation. The results of the two radiographic measurements were compared with intrasurgical measurement by Dunnett test.Results: Conventional PA radiographs underestimated the depth of lesion in comparison with clinical measurements. Linear measurements by the two observers did not show any significant difference between digitized radiographs and clinical dimensions, but measurements by the third observer underestimated the depth of the lesion in digitized radiographs in comparison with clinical measurements. However, the amount of underestimation was less than that of measured by conventional PA radiographs.Conclusion: In this study, the validity of digitized radiographs was more than that of the conventional PA radiographs in comparison with clinical measurements (Gold standard). Key words: Conventional PA radiograph, Periodontal osseous defect, Digitized radiograph