Purpose: The primary objective of the present controlled study was to determine the accuracy and precision of intraoral radiography in assessing interproximal bone defect morphology in patients suffering from periodontal disease as well as in patients with peri-implantitis. A secondary objective was to evaluate the possible impact of clinical experience on accuracy and precision. Materials and methods: The study sample comprised a total of 99 interproximal bony defects (40 patients) needing surgical treatment. Forty-nine defects were periodontal (17 patients), while the remaining 50 were peri-implant defects (23 patients). Following reflection of a mucoperiosteal flap and removal of granulation tissue, the type of bone defect as classified by Goldman and Cohen (1958) was determined. This intrasurgical registration was considered the true bone defect morphology. An intraoral radiograph was taken for each interproximal site. Twenty clinicians determined the bone defect morphology on each intraoral radiograph twice, with a washout period of 3 months. Results: Using the Goldman and Cohen (1958) classification, the overall accuracy of intraoral radiography in assessing interproximal bone defect morphology was slight for teeth/implants (κ = 0.132; 95% CI: 0.091 to 0.173/κ = 0.126; 95% CI: 0.091 to 0.162). Duplicate evaluation indicated fair precision (κ = 0.369; 95% CI: 0.308 to 0.430/κ = 0.355; 95% CI: 0.230 to 0.414). Pooling one-, two- and three-wall defects into one category had a positive impact on accuracy (κ = 0.254; 95% CI: 0.201 to 0.307/κ = 0.387; 95% CI: 0.340 to 0.435), as well as on precision (κ = 0.504; 95% CI: 0.423 to 0.584/κ = 0.560; 95% CI: 0.463 to 0.657). A significant difference between experienced clinicians and trainees was not found (P ≥ 0.285). Conclusions: Intraoral radiography lacks accuracy for assessing interproximal bone defect morphology around teeth and implants. Clinical experience does not seem to influence this. Keywords: bone defect, bone morphology, intraoral radiography, peri-implantitis, periodontal disease