The present research quantified multisensory integration (MSI) in young adults with and without attention-deficit/hyperactivity disorder (ADHD). MSI is a form of sensory processing where the nervous system integrates stimuli occurring together in time and/or space (Paraskevopoulos & Herholz, 2013). Multiple brain regions involved in MSI have also been reported to be altered in individuals with ADHD (Proal et al., 2011), which poses the question whether those with ADHD experience altered MSI. Participants completed a two-alternative forced-choice discrimination task while whole-head 64-electrode electroencephalography (EEG) was recorded (10 ADHD; 12 Neurotypicals). Stimulus presentation conditions were auditory-alone (~300 ms duration; verbalization adjusted to comfortable volume per participant), visual-alone (250 ms duration; red, blue, or green-filled circle on black background), or a semantically congruent audiovisual. stimulus. The Principle of Superposition of Electrical Fields was used to assess MSI via EEG (Brandwein et al., 2011). The ADHD group demonstrated significantly shorter response times to each stimulus type (P = 0.048) and both groups responded most accurately to the auditory-alone stimulus compared to the visual-alone stimulus (P < 0.001). EEG analysis showed MSI occurring in both groups (P = 0.046) from 110-130 ms post stimulus over parietal occipital brain regions. However, the ADHD group showed greater MSI at this latency and brain region (P = 0.033). This is the first work to suggest that young adults with ADHD process audiovisual multisensory information differently during a complex RT task than neurotypical controls, and this may be related to the various altered neurological structures shown in previous research.