Although ADHD is a highly heterogeneous disorder, some children experience difficulties not just with inattention and hyperactivity-impulsivity, but also with co-occurring emotional problems. This includes a group with elevated callous-unemotional (CU) traits and a lack of empathy. While the presence of CU traits in ADHD is well-documented, the neurophysiological mechanisms remain unclear. Here, we hypothesize that CU traits in ADHD are associated with blunted neurophysiological response to negative emotional stimuli.