Psycholinguistic studies dealing with Alzheimer's disease (AD) commonly consider verbal aspects of language. In this paper we investigated both verbal and non-verbal aspects of speech production in AD. We used pauses and hesitations as markers of planning difficulties and hypothesized that AD patients show different patterns in the process of discourse production. We compared the distribution, the duration and the frequency of speech dysfluencies in the spontaneous discourse of 20 AD patients with 20 age, gender and socioeconomic matched healthy peers. We found that patients and controls differ along several lines: patients' discourse displays more frequent silent pauses, which occur more often outside syntactic boundaries and are followed by more frequent words. Overall patients show more lexical retrieval and planning difficulties, but where controls signal their planning difficulties using filled pauses, AD patients do not.