Oppositional defiant disorder (ODD) occurs in about 25% of children with an inattentive presentation and 50% of those with a combined presentation. It is characterised by angry or irritable mood, argumentative or defiant behavior and vindictiveness which are age-inappropriate. Conduct disorder (CD) occurs in about 25% of adolescents with ADHD. It is characterised by aggression, destruction of property, deceitfulness, theft and violations of rules. Adolescents with ADHD who also have CD are more likely to develop antisocial personality disorder in adulthood. Brain imaging supports that CD and ADHD are separate conditions, wherein conduct disorder was shown to reduce the size of ones temporal lobe and limbic system, and increase the size of ones orbitofrontal cortex, whereas ADHD was shown to reduce connections in the cerebellum and prefrontal cortex more broadly. Conduct disorder involves more impairment in motivation control than ADHD. Intermittent explosive disorder is characterised by sudden and disproportionate outbursts of anger and co-occurs in individuals with ADHD more frequently than in the general population.Anxiety and mood disorders are frequent comorbidities. Anxiety disorders have been found to occur more commonly in the ADHD population, as have mood disorders (especially bipolar disorder and major depressive disorder). Boys diagnosed with the combined ADHD subtype are more likely to have a mood disorder. Adults and children with ADHD sometimes also have bipolar disorder, which requires careful assessment to accurately diagnose and treat both conditions.Sleep disorders and ADHD commonly co-exist. They can also occur as a side effect of medications used to treat ADHD.
To be considered, several symptoms must have appeared by the age of six to twelve and occur in more than one environment (e.g. at home and at school or work). The symptoms must be inappropriate for a child of that age and there must be clear evidence that they are causing social, school or work related problems.The DSM-5 and the DSM-5-TR also provide two diagnoses for individuals who have symptoms of ADHD but do not entirely meet the requirements. Other Specified ADHD allows the clinician to describe why the individual does not meet the criteria, whereas Unspecified ADHD is used where the clinician chooses not to describe the reason. International Classification of Diseases
In the eleventh revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) by the World Health Organization, the disorder is classified as Attention deficit hyperactivity disorder (with the code 6A05). The defined subtypes are similar to those of the DSM-5: predominantly inattentive presentation (6A05.0); predominantly hyperactive-impulsive presentation(6A05.1); combined presentation (6A05.2). However, the ICD-11 includes two residual categories for individuals who do not entirely match any of the defined subtypes: other specified presentation (6A05.Y) where the clinician includes detail on the individuals presentation; and presentation unspecified (6A05.Z) where the clinician does not provide detail.In the tenth revision (ICD-10), the symptoms of hyperkinetic disorder were analogous to ADHD in the ICD-11. When a conduct disorder  (as defined by ICD-10) is present, the condition was referred to as hyperkinetic conduct disorder.