ADHD has been identified as an extremely heterogeneous disorder from a clinical perspective, with high rates of comorbidity with other disorders. It is estimated that around 40–80% of children with ADHD have an associated comorbid condition, which often persists into adulthood.

In children and adolescents, the most common comorbid disorders with ADHD are oppositional defiant disorder, specific learning disorder, anxiety disorder, and sleep disorder. In adulthood, the most frequent psychiatric comorbidities with ADHD are depression, anxiety disorder, bipolar disorder, sleep disorders, and substance use disorder.

In addition, other difficulties associated with the disorder are observed that negatively interfere with the family, school and social sphere: difficulties in social relationships, learning difficulties and deficit in emotional self-regulation.