IntroductionThere have been few studies comparing the effects of giving both versions of a cognitive test to bilingual subjects. This study examined the test performances of Irish and English language versions of the MMSE in a bilingual older hospital population in Ireland. Materials and methodsEstablished principles, including back-translation, were used to develop an Irish version of the MMSE. This version and the English MMSE were administered a few days apart to 134 hospital patients aged 75 years or more. All subjects were independently assessed for the presence of dementia. ResultsSignificantly higher scores were found on the Irish MMSE (mean: 21.9 [standard deviation: 6.8] versus 21.3 [7.1], P=0.001), although 21 (16%) subjects scored higher on the English version. The difference was greatest in favour of the Irish MMSE for the 44 subjects who had been monolingual Irish speakers up to 5 years old (20.9 [6.3] versus 19.1 [6.5], P=0.001). Forty (30%) subjects had dementia. The area under receiver-operating characteristic curves for detection of dementia was significantly higher for the Irish version (0.96 [standard error: 0.013] versus 0.94 [0.016], P=0.009). ConclusionsThere are significant individual and group differences when older bilingual patients are administered different language versions of a cognitive test. These results support the need for different language versions of such tests.