The study examined individual contributions of visual and auditory information on multisensory integration across the life span. In the experiment, children, young adults, and older adults participated in a variant of the Sound-Induced Flash Illusion where participants had to either ignore beeps and report how many flashes they saw or ignore flashes and report how many beeps they heard. Collapsed across age, auditory input had a stronger effect on visual processing than vice versa. However, relative contributions of auditory and visual information interacted with age, with young adults showing evidence of auditory dominance (only auditory input affected visual processing), whereas, multisensory integration effects were more symmetrical in children and older adults. The findings have implications for many tasks that require the processing of multisensory information.