Recently, a number of recent reports have reported cases of bone marrow defect (BMD) in the mandible. Among the diseases seen by BMD in radiographs, focal osteoporotic bone marrow defect(FOBMD) is asymptomatic, which is discovered incidentally and localized radiolucency. Because it varies in size, shape, trabeculae and border definition, it needs to biopsy to differential diagnose other intraosseous lesions that show radiological bone marrow defects. This cases report discusses the pre-operation considerations in patients planning to implant the mandible and suspected to have FOBMD in radiographs. The following 4 cases in Dental Hospital of Wonkwang University were taken in panoramic and Cone beam computed tomography(CBCT). In all cases, there were radiolucent lesion diagnosed with FOBMD under radiologic differential diagnosis. In three of cases the implant were placed without treatment plan change and one case changed the treatment plan with removable partial denture. BMD is anatomical state that can affect primary stability of implant fixture. During implant placement, it can lead to unexpected results that fixture is fallen into BMD and the nerve may be damaged after implant fixture removal to cause hyperesthesia. Preoperative diagnosis of these lesions by differential diagnosis with panoramic and CBCT can prevent the complications by changing the treatment plan or paying attention to the manipulation during surgery.