Abstract
1. A case of spontaneous posterior interosseous paresis is reported. It is suggested that the cause was replacement fibrosis secondary to local ischaemic damage from unremembered minor trauma. 2. In a patient with a posterior interosseous nerve paresis examination may reveal a space-occupying lesion near the elbow along the course of the nerve thus compressing it. Recovery may be expected after its removal. Consequently the nerve should be explored before resort to tendon transfers.