There is growing evidence that AD consists of different subtypes, and that language is a pertinent factor to identify a subgroup with a fast rate of cognitive decline. We report the first results of a longitudinal study in which we compared two groups of patients with probable AD. The main result showed that a subgroup with stable MMSE scores during a 1-year follow-up period had an impairment in language domains which are usually preserved until an advanced stage of the disease. It is proposed that this group may correspond to a variety of AD who, in addition to symptoms of AD, present characteristics of primary progressive aphasia. In other respects, we underscore that the high loading in language-mediated tasks of the MMSE makes it a poor index to accurately measure the rate of cognitive decline.