Autism spectrum disorders (ASD) are pervasive developmental disorders characterized by impairments in language development and social interaction, along with restricted and stereotyped behaviors. These behaviors often include atypical responses to sensory stimuli; some children with ASD are easily overwhelmed by sensory stimuli, while others may seem unaware of their environment. Vision and audition are two sensory modalities important for social interactions and language, and are differentially affected in ASD. In the present study, 16 children and adolescents with ASD and 16 typically developing (TD) participants matched for age, gender, nonverbal IQ, and handedness were tested using a mixed event‐related/blocked functional magnetic resonance imaging paradigm to examine basic perceptual processes that may form the foundation for later‐developing cognitive abilities. Auditory (high or low pitch) and visual conditions (dot located high or low in the display) were presented, and participants indicated whether the stimuli were “high” or “low.” Results for the auditory condition showed downregulated activity of the visual cortex in the TD group, but upregulation in the ASD group. This atypical activity in visual cortex was associated with autism symptomatology. These findings suggest atypical crossmodal (auditory‐visual) modulation linked to sociocommunicative deficits in ASD, in agreement with the general hypothesis of low‐level sensorimotor impairments affecting core symptomatology. Autism Res 2017, 10: 130–143. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.