Background: Idiopathic osteosclerosis (IOS) refers to lesions of the jaw bone. The present study was undertaken to determine the prevalence of IOS in a group of diabetes mellitus (DM) patients by radiographic evaluation and to investigate the relationship between the findings in relation to age, gender, and localization. Methods: Panoramic radiographs and clinical information for 832 DM patients were examined to identify IOS. Statistical analyses were performed using chisquare test. Results: In total, 60 IOS lesions were identified in 48 patients. The prevalence of IOS in DM patients was 5.8%. All the IOS lesions were detected in the mandible. Twenty-six IOS lesions were associated with root apex and 34 lesions were not associated with tooth. IOS occurred more commonly in the fourth (25.0%) and fifth (28.3%) decades of DM patients. In addition, 27 (53.3%) and 21 (35%) IOS lesions were observed in the premolar and molar area of mandible, respectively. Conclusions: In DM patients, the frequency of IOS is similar to that in the general population and the relatively prevalent location for IOS is the mandibular premolar region. IOS lesions can arise at any age without sex predilection. Additionally, our findings support the theory that IOS is a variation of normal bone development unrelated to a local stimulant.