In monolinguals, not only cortical areas but also specific subcortical structures are crucial for language and speech processing. While the role of the left basal ganglia in monolingual aphasia has been defined, its relevance in bilingual and polyglot aphasia is still unknown. Data have now been obtained on a patient who, following an ischaemic lesion not involving cortical structures and mainly confined to the left basal ganglia, showed severe impairments in mother tongue production, with significantly better performance in her hardly spoken second language. This dissociation remained stable for over a year and was observed both in spontaneous speech and in translation tasks. This pattern of linguistic performance, which has never been described in relation to subcortical lesions, suggests that the left basal ganglia play a relevant role in the output of a highly automatized language.