A longitudinal study of repetition in Alzheimer's disease involving 24 patients and 35 controls over 3 years of evaluation is reported. A number of issues are addressed: Repetition ability in AD patients over time, the relationship between overall severity of dementia and performance on repetition tasks, the resemblance between the language of early AD patients and transcortical sensory aphasia symptoms, the dependence on short-term memory of repetition in Alzheimer's Disease, the occurrence of linguistic processing during repetition of an oral message, and the bearing of repetition performance in AD on the notion that imitative responses index linguistic knowledge, particularly syntax. The analysis of the collected data suggests that patients with relatively mild AD perform sentence repetition well, and that this ability deteriorates over time, but that in a majority of patients, repetition remains better preserved than many other skills. AD patients do not seem to demonstrate a transcortical aphasia. Short-term memory, auditory comprehension at least to the level of retaining the gist of the sentence, and knowledge of syntax are implicated as explanations for the repetition ability in the face of a more general deterioration of function.