This paper presents research based on the discourse analysis of seven extempore simulated consultations between practising General Medical Practitioners and non-English speaking volunteer patients, with language-switching provided by educated but professionally untrained native speakers of the foreign language. The research project set out to examine how information is lost to both doctor and patient in the language-switching process. The results highlight the importance of appropriate interlocutor roles being occupied by all parties, as well as the dangers inherent in a lack of common ground within the transaction. The language pair used in the data is English-Spanish, but the results are discussed as applicable by extrapolation to any language pair. The findings highlight the risks to all parties of dysfunctional communications across language and culture. Cross-language communication is shown to be complex, and highly trained doctors' skills blunted by malfunctions in language-switching. Information is lost in such malfunctioning encounters, to the detriment of effective medical practice.