Differences in attentional and impulse control may underlie the increased impairment associated with youth with ADHD and comorbid anxiety (ADHD+ANX) compared to youth with ADHD without anxiety; however, findings from studies using behavioural and self-report measures have been mixed. This study addressed this issue by exploring the impact of the addition of anxiety on attentional and impulse control at a neural level, using event-related potentials (ERPs). Youth aged 11 to 17 with ADHD without anxiety (n = 34) and ADHD+ANX (n = 33) completed a Go/No-Go and Selective Auditory Attention task. Results indicated that the addition of anxiety in youth with ADHD was associated with enhanced early attentional processing, as well as stronger activation of impulse control, as exhibited by greater EFP and N2 amplitudes, respectively. Future directions and clinical implications of these results are discussed.