The objective of this study was to investigate relationships between caregiver-reported sensory processing abnormalities, and the physiological index of auditory over-responsiveness evaluated using acoustic startle response measures, in children with autism spectrum disorders and typical development. Mean acoustic startle response magnitudes in response to 65-105 dB stimuli, in increments of 10 dB, were analyzed in children with autism spectrum disorders and with typical development. Average peak startle latency was also examined. We examined the relationship of these acoustic startle response measures to parent-reported behavioral sensory processing patterns in everyday situations, assessed using the Sensory Profile for all participants. Low-threshold scores on the Sensory Profile auditory section were related to acoustic startle response magnitudes at 75 and 85 dB, but not to the lower intensities of 65 dB. The peak startle latency and acoustic startle response magnitudes at low-stimuli intensities of 65 and 75 dB were significantly related to the low-threshold quadrants (sensory sensitivity and sensation avoiding) scores and to the high-threshold quadrant of sensation seeking. Our results suggest that physiological assessment provides further information regarding auditory over-responsiveness to less-intense stimuli and its relationship to caregiver-observed sensory processing abnormalities in everyday situations.