So once a child has been diagnosed with ADHD, how do you determine its severity? It is not based on how long the child has been sick and how many abnormal manifestations there are, but mainly on how much damage the disease has done to the child and how much it has affected the child’s life, learning and social functioning. Mild: there is often no functional impairment, severe: there is severe functional impairment. Moderate: their functional impairment is somewhere in between. Xiaoyan Lu, Department of Neurology, Beijing Children’s Hospital