Aim: To assess the diagnostic performance of Cone beam computed tomography in the detection of secondary carious lesions under composite resin restorations. Objectives: To assess the diagnostic accuracy of cone-beam computed tomography (CBCT) in the detection of secondary carious lesions under composite resin restorations. Materials and methods: 50 Extracted human permanent posterior teeth were collected and primary cavities were created. Then all the samples were randomly divided into two groups; Group A- study group (n=25) and Group B- control group (n=25). Group A included artificially created defects mimicking secondary caries under primary cavities restored with composite restorations; Group B included primary cavities restored with composite restorations. CBCT scans of all the teeth were taken and evaluated by 3 observers for the presence of secondary caries. Results: Sensitivity was found to be 82.6% and specificity as 56%. ROC curve was plotted which was obtained as 0.716. Conclusion: Due to less specificity CBCT has a limited role in detection of secondary caries under composite restoration.