The term “coexisting disorders” is also known as “co-morbidities”, which means that they are different from co-occurring disorders and have the same root. In other words, there is a common family susceptibility in genetics, and it coexists with ADHD. It is often difficult to distinguish between the two because of the daily manifestation of “I have you, you have me”. It is important to emphasize that as soon as coexisting disorders appear, especially the earlier the onset, the greater the likelihood that ADHD will become complex and difficult to treat, and that treatment of coexisting disorders must be the mainstay in order for ADHD to improve. Therefore, timely detection and identification of coexisting disorders is very important. The most common coexisting disorders are the following: 1. obsessive-compulsive disorder (OCD): including a variety of obsessive-compulsive ideas and behaviors that appear repeatedly in thoughts and actions alone or at the same time, knowing that it is not right, but can not stop, never get rid of, sometimes very painful self-harming behavior such as biting the tongue, biting fingers, damage to the skin, disfigurement, etc. often leaving infections or scars, and even reveal suicidal thoughts that do not want to live. This must be highly vigilant to prevent accidents. 2, conduct disorder (Cn) and oppositional defiant disorder (ODD): as the name implies, both have anti-social tendencies, and should not be ignored, many parents often mistakenly believe that this performance is not a pathology, especially for ODD, thought that the child is just stubborn and scolded to suppress, but the result is that the condition is aggravated. 3, learning disabilities (LD): is cognitive impairment, mainly dyslexia and math difficulties, can seriously affect academic performance mood disorders (MD): mainly depression and poor mood, adult-type alternating depression – mania can also be in children and adolescents onset, and the relationship with multiple tics is not clear. 4. Anxiety (AD): mainly fear and anxiety, such as fear of separation from loved ones, fear of accidents to loved ones, fear of going to school, excessive fear of strangers and social interaction for a long time, and even daily worry and anxiety about the future. 5.Autism and related disorders: including language disorders and Aspergre’s syndrome which is the same as autism. 6.Attention deficit hyperactivity disorder (ADIID): It is characterized by inattentiveness and/or hyperactivity and impulsivity, commonly known as pediatric hyperactivity disorder.