1. A case of osteoid osteoma which recurred twice after block excision is reported.

2. It is postulated that recurrence is almost certainly caused by incomplete removal of the nidus, either by curettage or by incomplete block excision.

3. Why curettage is successful in most cases but not in others is obscure, but it may be that the arterial supply to the tumour is interrupted.

4. Block excision with adequate radiographic control to ensure its completeness is the treatment of choice.