The auditory startle reaction to an unexpected loud stimulus is regarded as a brainstem reflex originating in the nucleus reticularis pontis caudalis and being distributed up the brainstem and down the spinal cord along slowly conducting pathways. Auditory startle responses (ASR) have been reported absent or reduced in progressive supranuclear palsy (PSP), and delayed in Parkinson's disease (PD), but normal in multiple-system atrophy (MSA). For the first time we studied ASR in patients fulfilling the clinical criteria of dementia with Lewy bodies (DLB) (n = 8), a neurodegenerative disorder characterized by cortical and subcortical depositions of Lewy bodies resulting in parkinsonism and progressive cognitive decline. For comparison, we also investigated patients with PD (n = 10), MSA (n = 7), PSP (n = 10), and age-matched healthy controls (n = 10). ASR were elicited by binaural high-intensity auditory stimuli. Surface electromyographic activity was simultaneously recorded from facial, upper, and lower extremity muscles. For each muscle, we assessed response probability and measured latency, amplitude, duration, and habituation rate. Patients with DLB had fewer and abnormally delayed ASR of low amplitude and short duration in extremity muscles compared to healthy controls. Furthermore, we confirm and extend previous findings of abnormal ASR in PSP and PD, and also demonstrate exaggerated ASR in extremity muscles of MSA patients. The different patterns of ASR abnormalities may reflect distinct types of brainstem dysfunction in DLB, PD, MSA, and PSP. Mov. Disord. 16:62–71, 2001. © 2001 Movement Disorder Society.