Metaphyseal fibrous defects are cystic lesions filled with fibrous tissue and are usually eccentrically located in the metaphyses of the long bones of the extremities of children and young adults. The lower extremities are most often involved. Histologically these defects are filled with whorls and sheets of fibrous tissue, varying numbers of multinucleated giant cells, and a few foam cells. The absence of new-bone formation is a constant finding. These lesions apparently arise as a result of some unknown process in which a small area of the epiphyseal plate intermittently produces fibrous tissue instead of bone. It would appear that many of these lesions may be extruded from the bone in the process of remodeling of the metaphysis during bone growth.