Bone marrow edema, which cannot be seen by direct graphy or computed tomography, is a pathological condition which is identified after the routine usage of magnetic resonance imaging (MRI). It may be seen in many different diseases ranging from trauma-induced bone contusion to neoplastic lesions. For this reason, differential diagnosis should be made promptly and carefully. Whether bone marrow edema syndrome (bone marrow edema without any other accompanying pathology) represent a distinct disease or is a subtype of osteonecrosis remains controversial. This pathology which is also called as algodystrophy, transient osteoporosis or transient bone marrow edema syndrome is a self-limited disease. There are no findings at direct graphy at the early stages of the disease; however, local osteopenia is seen in the advanced stage. Diagnosis is established by MRI. Classical bone marrow edema syndrome patient is 30-60-year-old male who suffers from pain at a single bone of one joint. However, it may also be seen at 20-40-year-old females who are at their last trimester of pregnancy. The suggested treatment modalities are medical applications, conservative treatments and core decompression. The pathophysiology of bone marrow edema syndrome and its relation with avascular necrosis has not been clarified distinctly yet. However, the present consensus of opinion is that bone marrow edema syndrome and avascular necrosis may have a common pathophysiology but they are different with respect to the early potential for reversibility.