The evaluation of bone marrow of patients treated for cancer is complicated by age-related changes in the distribution of normal (red) and fatty (yellow) marrow and by the changes induced by treatments. The treatments used in oncology modify pathological marrow but also normal marrow and may sometimes lead to complications. The knowledge of bone marrow physiological status and post-therapeutic patterns is important for the interpretation of marrow disorders and effects of therapy. After radiation therapy, the signal intensity of normal bone marrow depends on the dose delivered and the interval between the treatment and the MR study. During the first two weeks of fractionated irradiation (after a dose of 30 Gy) there is no definite change in the appearance of the marrow on T1W and T2W images. On the STIR images there is an increase in signal intensity apparently reflecting early bone marrow oedema. After three weeks, fatty replacement begins, the marrow shows an increasingly heterogeneous signal and the vertebral body shows a prominence of the signal from central marrow fat on T1W images. Six weeks after therapy, there are two distinct types of late marrow pattern: homogeneous fatty replacement or a band-like pattern (sandwich vertebral body). Marrow regeneration is more likely to occur in children than in adults and when a large volume of marrow is irradiated than when radiation therapy is localised [1] . Bone marrow which received 50 Gy is definitively damaged and exhibits a fatty signal on MR images. This pattern is due to decreased cellularity associated with loss of bone trabeculae [2] .