The clinical picture associated with various lesions of the thalamus is described. The effects of surgical Iesion in thalamus are reviewed in light of the author''s experience with VL thalamotomy, and in unilateral and bilateral pulvinectomy. The relation of thalamus to language and cognition is complex. True aphasia does not appear to follow thalamic lesion but rather there is a ‘withering’ of the language mechanism to a final state of mutism. Evidence is also presented for a ‘mass action’ at the thalamic level.