Several patients with 'progressive loss of speech output' or 'progressive anarthria' of degenerative origin have been reported in the literature. We report 5 clinical cases with slowly progressive loss of speech output and initially no deficit in other cognitive domains. The early clinical features were analysed in an attempt to identify the anatomo-functional systems implied in the degenerative process. The first phase of the disorder was characterised by impaired articulation consistent with speech apraxia, telegraphic style and a difficulty to elaborate a series of orofacial or hand movements. It is argued that these symptoms result from an impairment of complex motor processing due to dysfunction of the ventral premotor system. In the second phase, a decrease in spontaneous speech and self-initiated action was combined with exaggerated dependency on external stimuli, interpreted as dysfunction of the dorsal premotor system. We suggest that the neuropsychological profile of the disorder may result from progressive degeneration of the premotor cortex.