Cerebral lesions may alter the capability of bilingual subjects to separate their languages and use each language in appropriate contexts. Patients who show pathological mixing intermingle different languages within a single utterance. By contrast, patients affected by pathological switching alternate their languages across different utterances (a self contained segment of speech that stands on its own and conveys its own independent meaning). Cases of pathological mixing have been reported after lesions to the left temporoparietal lobe. By contrast, information on the neural loci involved in pathological switching is scarce. In this paper a description is given for the first time of a patient with a lesion to the left anterior cingulate and to the frontal lobe-also marginally involving the right anterior cingulate area-who presented with pathological switching between languages in the absence of any other linguistic impairment. Thus, unlike pathological mixing that typically occurs in bilingual aphasia, pathological switching may be independent of language mechanisms.