This event-related potential study focused on neural correlates of inhibitory affective control in attention-deficit hyperactivity disorder (ADHD). Sixteen boys with ADHD and 16 healthy boys underwent an emotional Go/NoGo task with pictures of facial expressions from the categories anger, sadness, happiness, and neutral. The participants were instructed to execute or withhold a motor response to specific emotions. Patients relative to controls displayed a severe impairment in response inhibition toward anger cues, which was accompanied by a reduced P300 amplitude (positive voltage deflection about 300 ms after picture onset). The control group showed a P300 differentiation of the affective categories that was absent in the ADHD group. The pronounced anger-processing deficit in ADHD patients might be linked to their interpersonal difficulties and should be addressed in psychotherapy.