The author shows, by means of histologically verified cases, that, in the development of the disease process, the small central nidus may increase through further dcstruction until it may be larger than the cross section of the normal skeleton at a given point. Two clinically and roentgenographically typical, but histologically unverified, cases give presumptive grounds for concluding that the natural course of the disease leads to spontaneous healing. This development appears contradictory to the claim that the disease is caused by bone infarction, and is hardly compatible with the generally accepbed definition of a tumor.