Osteoporotic bone marrow defect （OBMD） is a rare benign jaw lesion consisting of hematopoietic bone marrow, which results in a focal bone defect. The present report describes a case of OBMD in the mandibular molar region of a 53 year-old-woman. A panoramic radiograph showed the presence of an undefined round,thumb-sized radiolucent lesion in the lower left first molar region. The density inside of the lesion was −37.7 Hounsfield units on CT scanning, suggesting fat tissue. The biopsy specimens revealed fat tissue with thin bone trabeculae and hematopoietic cell infiltration. The clinical course has been uneventful without any treatment for 4 years.
