Abstract
1 . Six patients have been presented in whom an established diagnosis of non-osteogenic fibroma of bone was made. Metaplastic bone was identified within the tumour tissues.
2. Three other patients are reported in whom the diagnosis appeared to be, on radiological and histological grounds, either fibrous dysplasia or non-osteogenic fibroma.
3. This evidence has convinced the author that the two lesions are frequently not distinctive and that they are, in fact, closely related. Because the natural history of the two conditions, especially in their simple or monostotic form, is also the same, there is good reason to consider them as varying histological manifestations of the same pathogenetic process.