Thirteen cases of idiopathic common peroneal nerve palsy were reviewed and the clinical presentation and course evaluated. Incomplete nerve palsy of unknown aetiology has a good prognosis and all the patients in this group made a full recovery without surgical intervention. Those presenting with a clinically and electrophysiologically complete lesion made no recovery, despite surgical intervention in two cases. It is suggested that these lesions can safely be treated conservatively as long as there is no identifiable cause.