The Mini-Mental State Examination (MMSE) is a rapid, easy-to-administer test for the assessment of cognition functions. It is widely used in clinical practice and in applied research. In this study, we aimed to establish a standard for the Mexican population similar to the ones produced for other relevant populations. We also analysed the effects of demographic variables which regularly induce bias in responses on performance tests, and then, on the basis of the results, implemented a series of corrections to the MMSE to compensate for the usual effects of age and years of formal education. We thus generated a new scale, the adjusted MMSE (AMMSE). We established the maximum sensitivity point to discriminate between the normal population and subjects diagnosed with dementia (vascular and Alzheimer’s). The study provides sensitivity and specificity estimates of this subject-standardized tool in order to reduce the probability of false positives and negatives in the Mexican population.