This study assessed sensory processing differences between 24-month infants at high-risk of autism spectrum disorder (ASD), each with an older sibling with ASD, and low-risk infants with no family history of ASD. Sensory processing differences were assessed using the Infant/Toddler Sensory Profile, a parent-reported measure. Groups were compared based on 3-year outcomes: (a) high-risk infants subsequently diagnosed with ASD; (b) high-risk infants without an ASD diagnosis; and (c) low-risk infants without an ASD diagnosis. Analyses showed that high-risk infants diagnosed with ASD have more difficulty with auditory processing (i.e., responses to auditory stimuli) and lower registration (i.e., lacking sensation awareness) compared to controls. Thus, behavioral responses to sensory input represent early risk markers of ASD, particularly in high-risk infants.