A person with ADHD has a chronic level of inattention, impulsive hyperactivity, or both such that daily functioning is compromised. The symptoms of the disorder must be present at levels that are higher than expected for a person's developmental stage and must interfere with the person's ability to function in different settings (e.g., in school and at home). A person with ADHD may struggle in important areas of life, such as peer and family relationships, and school or work performance. 

Three types of ADHD have been established according to which symptoms are strongest in the individual. These types are described below:

1. Predominantly Inattentive Type: It is hard for the individual to organize or finish a task, to pay attention to details, or to follow instructions or conversations. The person is easily distracted or forgets details of daily routines.
    

2. Predominantly Hyperactive-Impulsive Type: The person fidgets and talks a lot. It is hard to sit still for long (e.g., for a meal or while doing homework). Smaller children may run, jump or climb constantly. The individual feels restless and has trouble with impulsivity. Someone who is impulsive may interrupt others a lot, grab things from people, or speak at inappropriate times. It is hard for the person to wait their turn or listen to directions. A person with impulsiveness may have more accidents and injuries than others.
    

3. Combined Type: Symptoms of the above two types are equally predominant in the person.

As many as half of those with ADHD also have other mental disorders. These comorbidities of ADHD (other disorders that occur along with ADHD) can make it harder to diagnose and treat ADHD. They may also present further challenges to the individual with ADHD.

Used by mental health professionals, the DSM-IV-TR provides criteria for diagnosing ADHD. This diagnostic standard helps ensure that people are appropriately diagnosed and treated for ADHD. Using the same standard across communities will help determine the public health impact of ADHD. 

Treating ADHD can be done through medical or behavioral therapies, or a combination of the two.