purpose: to identify language deficits in a group of elderly patients with dementia in tasks of free lexical retrieval, lexical retrieval with orthographic and semantic criteria, interpretation of metaphors and of narrative discourse, from the montreal communication evaluation battery - mac battery, as well as to verify the frequency of deficits. methods: participants were 13 patients with mild to moderate dementia, treated at the neurology sector of the ambulatory of movement disorders and dementia of the hospital santa clara of the irmandade santa casa de misericórdia de porto alegre (iscmpa). the neuropsychological assessment instrument was the mac battery, and the tasks were applied in the following order: free lexical retrieval, lexical retrieval based on orthographic criteria, lexical retrieval based on semantic criteria, interpretation of metaphors, and interpretation of narrative discourse. results: the group of patients with dementia showed impaired performance in all tasks from mac battery that were evaluated, with significant difference. furthermore, participants presented higher frequency of deficits, in descending order, in partial retelling of narrative discourse tasks (essential and present information), followed by the tasks of lexical retrieval with orthography and semantic criteria, and full retelling of narrative discourse. at least two patients showed deficits in some of the five tasks performed from the mac battery. conclusion: language evaluation using the mac battery allowed the verification of language processing deficits in elderly with dementia, characterizing that this instrument is also applicable to this clinical population.