OBJECTIVES. We examined whether children with and without autism spectrum disorder (ASD) differ in autonomic activity at rest and in response to auditory stimuli and whether behavioral problems related to sounds in everyday life are associated with autonomic responses to auditory stimuli. METHOD. We measured skin conductance (SC) at rest and in response to auditory stimuli as well as behavioral responses using the Sensory Processing Measure (SPM) Home Form. Participants were 25 children with ASD and 25 typically developing (TD) children, aged 5–12 yr. RESULTS. The ASD group had significantly higher resting SC and stronger SC reactivity to tones than the TD group. Correlations between SC and SPM indicated that more severe auditory behavioral difficulties were associated with higher sympathetic activation at rest and stronger sympathetic reactivity to sound. CONCLUSION. High sympathetic reactivity to sound may underlie the difficult behavioral responses to sound that children with ASD often demonstrate.