The use of the mother tongue relies on implicit memory procedures that are mainly controlled by subcortical structures. A second language depends on the integrity of the explicit memory system, largely subserved by cortical areas. Therefore, bilinguals can be considered as neurolinguistic models which contribute to the understanding of how the cortical and subcortical language systems communicate while maintaining independent functions. We describe a patient who developed an impairment of the mother tongue after an infarct of the caudate. During follow-up, a dramatic improvement of the mother tongue accompanied by worsening of the second language became evident after the extension of the ischemic lesion to the cortex.