Background: Age-related changes occur in the bone marrow from childhood to senility. These changes are exaggerated in patients with osteoporosis. Findings. The bone marrow is composed of ‘fatty’ marrow as well as ‘red’ or “functioning” marrow. Functioning marrow comprises hematopoietic, platelet, and immune system cells (lymphocytes, plasma cells, monocytes, etc.) cells. As the bone marrow is housed in a confined rigid space, any change in marrow fat content is mirrored by a reciprocal change in functioning marrow content. As marrow fat content increases as a feature of normal ageing, there is a corresponding reduction in functioning marrow content. This reduction in functioning marrow is a reflection of ‘immunosenescence’, i.e. a physiological age-related decline in the immune system that makes older subjects more susceptible to infection, cancer, and autoimmune disease and which limits the ability of the bone marrow to respond to increased demand in older subjects. Also functioning marrow, being more metabolically active, is the main driver of bone blood flow. The reduction in functioning marrow seen in older subjects is associated with reduced bone blood flow which, in turn, impairs fracture healing ability. This compromised fracture-healing capacity may, at a microscopic level, affect microfracture healing, leading to microdamage accumulation and eventual osteoporosis-related fragility fracture. Summary: MRI is an excellent means of non-invasively studying age-related bone marrow changes. Both the content as well as the composition of bone marrow can be studied in addition to bone perfusion and diffusion. As the bone marrow is the main reserve of red cell, platelet, and immune system cells, changes within the bone marrow have a systemic effect and vice versa. As such, age-related changes in the bone marrow are of considerable clinical relevance.