Objective: To provide a comprehensive description of motor speech function in behavioral variant frontotemporal dementia (bvFTD).Methods: Forty-eight individuals (24 bvFTD and 24 age-and sex-matched healthy controls) provided speech samples. These varied in complexity and thus cognitive demand. Their language was assessed using the Progressive Aphasia Language Scale and verbal fluency tasks. Speech was analyzed perceptually to describe the nature of deficits and acoustically to quantify differences between patients with bvFTD and healthy controls. Cortical thickness and subcortical volume derived from MRI scans were correlated with speech outcomes in patients with bvFTD.Results: Speech of affected individuals was significantly different from that of healthy controls. The speech signature of patients with bvFTD is characterized by a reduced rate (75%) and accuracy (65%) on alternating syllable production tasks, and prosodic deficits including reduced speech rate (45%), prolonged intervals (54%), and use of short phrases (41%). Groups differed on acoustic measures derived from the reading, unprepared monologue, and diadochokinetic tasks but not the days of the week or sustained vowel tasks. Variability of silence length was associated with cortical thickness of the inferior frontal gyrus and insula and speech rate with the precentral gyrus. Conclusions:One in 8 patients presented with moderate speech timing deficits with a further twothirds rated as mild or subclinical. Subtle but measurable deficits in prosody are common in bvFTD and should be considered during disease management. Language function correlated with speech timing measures derived from the unprepared monologue only. Neurology ® 2017;89:837-844 GLOSSARY ALS 5 amyotrophic lateral sclerosis; AMR 5 alternating motion rate; bvFTD 5 behavioral variant of frontotemporal dementia; CBD 5 corticobasal degeneration; CI 5 confidence interval; DDK 5 diadochokinesis; FTD 5 frontotemporal dementia; lvPPA 5 logopenic variant primary progressive aphasia; nvPPA 5 nonfluent variant primary progressive aphasia; PALS 5 Progressive Aphasia Language Scale; PPA 5 primary progressive aphasia; PSP 5 progressive supranuclear palsy; ROI 5 region of interest; SMR 5 sequential motion rate; svPPA 5 semantic variant primary progressive aphasia.