Introduction: This study compares the accuracy of panoramic radiography and CBCT in detecting and diagnosing mandibular apical lesions, analysing the effect of the thickness of the cortical bone on the radiological visibility of apical lesions. Methods: Digital images of 343 patients who had CBCT scans and panoramic radiographs were inspected for mandibular apical lesions. The dimensions of the lesion and the thickness of the cortical bone in the affected region were measured. Statistical analyses were made using statistical software (IBM SPSS 25, IBM, Armonk, NY, USA). Results: CBCT detected apical lesions around 115 teeth; 77 of these were also visible on a panoramic radiography. The differences between the two methods were statistically significant in the premolar and molar regions (McNemar test; p 0.001) but not in the anterior region (p = 0.063). For the size of the lesions no significant differences were found (Wilcoxon test; anterior, p = 0.60; premolar, p = 0.90; molar, p = 0.61). In the Mann-Whitney U test, buccal and palatal cortical thickness did not significantly influence the visibility of lesions in CBCT and panoramic measurements (buccal, p = 0.93; palatal, p = 0.15). Conclusion: Apical lesions seem to be much more readily visible on CBCT scans. The thickness of the cortical bone and the size of the lesions do not significantly influence the representation of apical lesions. Keywords: apical lesions, CBCT, cone-beam computed tomography, cortical bone thickness, panoramic radiography