1. Four cases of myositis ossificans circumscripta are presented. 2. It remains an obscure condition but there are characteristic clinical, radiological and microscopical features. 3. While the majority of cases arise as a direct result of injury, these four cases suggest that this is not always so ; the diagnosis from osteosarcoma, bone or joint infection may then be difficult. 4. Noble's classification (1924) of myositis ossificans is adequate and should be accepted. Confusion would be avoided if cases such as those presented here were included in the classification suggested.