Coming soon: AboutKidsHealth is getting a new look! Learn more Watch a video tour


When a person has more than one disease or health condition at the same time, this is called comorbidity. Comorbid conditions may be related:

  • One condition may cause another condition.
  • An underlying cause may make the person vulnerable to both conditions.

Comorbid conditions may also happen without being related.

Studies have shown high rates of comorbid conditions among children with ADHD, including anxiety, depression, Tourette’s syndrome, oppositional defiant disorder, conduct disorder, and learning disabilities. For this reason, diagnosing ADHD includes assessing the child for comorbid conditions. The tables below show the approximate percentage of individuals with ADHD who are diagnosed with each condition.

Table 1: Comorbid Mental Health Conditions

Mental Health Conditions % of children with ADHD who have comorbid condition
Anxiety/mood disorders 25% to 48%
Severe tics/Tourette's Disorder 11%
Oppositional Defiant Disorder 40% to 60%
Conduct Disorder 14% to 20%
Bipolar disorder 0.2%

Table 2: Comorbid Learning Disabilities

Learning Disabilities % of children with ADHD who have comorbid condition
Oral language disorders 8% to 30%
Reading disorder 15% to 40%
Mathematics disorder 10% to 25%
Written language expression unclear (clinical study suggests about 65%)
Developmental coordination disorder 40% to 60%
Jensen, Hinshaw et al. 2001; Carroll, Maughan et al. 2005; Reich, Neuman et al. 2005; Kessler, Adler et al. 2006

ADHD and mood disorders such as anxiety or depression

Most children are afraid, worried, or sad sometimes. These feelings usually pass quickly or are related to a specific event. However, when children's worries, fears, or sadness continue for a long time and affect their day-to-day lives, they may be part of a more serious problem.

Some studies suggest that anxiety and depression are more common in children with symptoms of inattention.

ADHD and anxiety disorders

Children with ADHD and anxiety disorder are "worriers." They may worry about:

  • their competence and performance in academics, athletics, and social situations
  • their behaviour
  • their parents or other close family members
  • what other people, including teachers and peers, might think about what they say or do
  • future events, such as appointments with doctors or dentists, tests at school, school trips, and new activities

They may not talk openly about their worries. Their anxiety may be shown in different ways, such as:

  • looking tense
  • nervous mannerisms such as nail biting, leg jiggling, breath holding, or gulping
  • not wanting to leave parents and come to school, or to leave the teacher and go out to the playground
  • constantly seeking reassurance about their performance
  • refusing to do what a parent or teacher asks them to do in order to avoid a new or challenging situation

Girls are slightly more likely than boys to have a comorbid anxiety disorder.

ADHD and depression

Children with ADHD and depression "carry the world on their shoulders." However, they rarely talk about what is bothering them. Instead, they may:

  • have a hunched, stooping posture and carry their head down with little eye contact
  • look pale, listless, sad, or tearful
  • rarely or never laugh when something funny happens
  • not appear to have fun or experience joy
  • prefer to spend time by themselves
  • have low self-esteem
  • perform poorly at school
  • think about or make comments to teachers, parents, or peers about killing themselves

ADHD and Tourette’s Syndrome

While children with ADHD often act impulsively, children with Tourette’s syndrome have frequently occurring behaviours which they are unable to control, called tics. These can include:

  • motor tics, like squinting or shrugging repeatedly, facial grimacing, and even more complex arm and leg movements
  • vocal tics, like throat clearing, repetitive noises, sniffing, or using profanity

Most children with Tourette’s syndrome (81%) also meet criteria for a diagnosis of ADHD. As a result, it has been suggested that Tourette’s syndrome may be a severe form of ADHD. Children with both Tourette’s syndrome and ADHD need a combination of treatment strategies.

ADHD and Oppositional Defiant Disorder or Conduct Disorder

Most children, including those with ADHD, sometimes refuse to do what adults want them to do. They may answer back, tell fibs, get angry, yell, stamp their feet, or even hit. These behaviours are part of normal development. Eventually, the child learns that they are not acceptable. However, if the child often misbehaves and the behaviour continues for a long time, the child may have Oppositional Defiant Disorder (ODD) or a more severe condition, Conduct Disorder (CD).

Some studies suggest that ODD and CD are more common in children with symptoms of hyperactivity and impulsivity.

Boys are about twice as likely as girls to have ODD or CD.

ADHD and Oppositional Defiant Disorder

Children with ADHD and ODD are "big reactors." They may:

  • throw things, stamp, yell at others, or have temper tantrums
  • talk back and refuse to back down or do what they are told ("You can't tell me what to do")
  • deliberately annoy other people by poking, pulling, or grabbing
  • never accept responsibility and blame others for their own misbehaviour
  • whine and complain about others ("It's not fair," "You never give me a chance," "He always does it to me")
  • hold grudges or try to "get back" at others

ADHD and Conduct Disorder

Children with ADHD and CD may:

  • have attacks of violent and uncontrollable physical aggression towards people or property
  • be verbally aggressive
  • be truant from school
  • lie
  • carry weapons such as knives
  • carry matches and often play with fire
  • "joy-ride" by stealing and using bicycles, motorcycles, or cars
    get in trouble with police more than once

Behaviour like this is serious. Children with suspected CD need professional help from someone with experience.

ADHD and learning disabilities

ADHD can cause a child to do poorly in school. However, poor school performance may also be caused by a learning disability (LD). Children with ADHD very often have a comorbid learning disability. Researchers have suggested that ADHD and learning disabilities may both be associated with the same weaknesses in working memory  and executive function .

Learning disabilities involve difficulties in processing information. Children who are diagnosed with a learning disability have normal intelligence but have problems in performing one or more scholastic skills:

  • reading
  • writing and spelling
  • mathematics

More specifically, LD refers to a deficit in one or more of the psychological processes involved in understanding or using spoken or written language. This underlying deficit will show itself in problems with listening, thinking, speaking, reading, writing, spelling, or doing mathematical calculations.

A learning disability may be suspected if:

  • the child learned to speak late
  • the child has a harder time learning nursery rhymes or songs than her peers
  • the child does worse than expected in one particular subject
  • there is a mismatch between the child's intelligence and her school performance

Learning and school problems are discussed in more detail in the "At School" section.

ADHD and Developmental Coordination Disorder

Children with ADHD often have Developmental Coordination Disorder (DCD) as well. DCD is suspected when a child has motor coordination that is much poorer than expected from the child's age and intelligence. Children with DCD may be slow to achieve motor milestones such as sitting, crawling, and walking; they may be clumsy and often drop things; they may do poorly at sports.

DCD affects many areas of a child's daily life. A child with DCD may have trouble getting dressed or riding a bicycle, or may do poorly at school because of poor handwriting.

We are still learning how best to help children with DCD.  

Peter Chaban, MA, MEd

Rosemary Tannock, PhD