Skip links and keyboard navigation

Intellectual disability

How common is intellectual disability?

Intellectual disability is the most common primary disability reported in Australia (about 3% of Australians have an intellectual disability).

According to the Australian Institute of Health and Welfare, more than 60% of people with intellectual disability in Australia experience severe or profound limitation in core daily living activities.

Intellectual disability is a developmental disorder characterised by:

  • intelligence limitations – an intelligence quotient (IQ) below 70. The average IQ is 100.
  • significant difficulty with daily living skills including self-care, self-direction, safety, communication and socialisation.

The majority of intellectual disability in Australian people results from genetic disorders such as Down syndrome, fragile X syndrome, Williams syndrome and Prader Willi syndrome.

People with intellectual disability have more trouble in learning new things, understanding concepts, solving problems, concentrating and remembering. The problems people with intellectual disability may experience change from person to person and depend on factors such as the presence of other disabilities and the person’s own unique personality.

Often children (0-6 years of age) are considered too young to receive a diagnosis of intellectual disability and instead ‘developmental delay’ is used to show that the child is experiencing difficulties in different areas of their skill development. If a young child has a ‘developmental delay’ that does not necessarily mean that they will be diagnosed with intellectual disability.

The main cause of intellectual disability is unknown. The most common causes include:

  • genetic conditions such as Down syndrome, fragile X syndrome, Williams syndrome and Prader Willi syndrome
  • problems during pregnancy such as infections or exposure to alcohol, drugs or other toxins
  • problems at birth
  • environmental factors such as exposure to poisons, lead or mercury
  • consequences of neglect, such as malnourishment or inadequate medical care
  • difficulties from health problems such as meningitis, measles or whooping cough.

While there is no cure for intellectual disability, early intervention, education and support can help people achieve happy, productive and fulfilling lives.

Early signs of intellectual disability

There are many signs of intellectual disability, such as:

  • in children, slowness in learning to sit, crawl or walk
  • delay in learning to talk or ongoing trouble with talking
  • poor attention capacity
  • limited planning or problem solving abilities
  • difficulty with understanding rules and instructions
  • behavioural and social problems
  • trouble with self-care tasks such as getting dressed, toileting and feeding themselves.

It is important to remember that people develop at different rates. Some are slower than others but catch up with time. However if you are concerned it is better to have your concerns checked than to wait and see.


Diagnosis is generally sought at a young age. Getting assessed and diagnosed with intellectual disability will give you access to a range of support, treatments and therapies, including early intervention services if the diagnosis was given to a child.

Diagnosis will help those affected and their families to better understand how development and functioning is affected by intellectual disability. It may assist to discuss and further explore a person’s learning and cognitive abilities, motor skills and health in general.

Some younger children may initially receive a diagnosis of developmental delay. This is because the major developmental changes that occur in the early years can make it hard to find out if they are temporary or permanent. Children with mild intellectual disability in particular may not receive a formal diagnosis of intellectual disability until after starting school when it is easier to decide if the child’s learning difficulty is permanent.

Some professionals may talk about IQ tests and use language to describe how well a person does on a range of test items. Tests may indicate that a person’s cognitive abilities and adaptive behaviour skills such as, personal care, communication and social skills fall into a mild, moderate, severe or profoundly intellectually delayed range when related to their peers.

Although IQ scores and other tests are used to guide the level of support a person will need, each person’s personality, coping skills, experiences, additional disabilities and type of family and community support, will influence life outcomes.

For many people diagnosed with intellectual disability, there can be other sensory and physical disabilities that make skills and strengths difficult to see, so it is important to explore different ways a person may be able to be supported to develop a wide range of skills.

  • Mild intellectual disability – a person with mild intellectual disability will have a 50 to 70 IQ score and will generally require some level of support in developing social, communication, play skills and self-care, as well as help to develop their fine and gross motor skills. Children with mild intellectual disability will benefit from additional learning support at school.
  • Moderate intellectual disability – a person with moderate intellectual disability will have a 35 to 50 IQ score and are likely to need support to learn. Children with moderate intellectual disability will need support to learn self-care and daily living tasks, and later independence will be improved with opportunities to learn and practice these tasks.
  • Severe or profound intellectual disability – a person with severe intellectual disability will have a 20 to 35 IQ score. A person with profound intellectual disability will have an IQ score up to 20. They benefit significantly from support from a young age and are likely to require ongoing support in all areas of their life, as well as therapy to develop and maintain fine and gross motor abilities.

When a child receives a diagnosis of intellectual disability a number of things will happen. The paediatrician will discuss the types of supports and services that will optimise the child’s development and a plan may be developed. The plan is about the child so parents and family members should be involved in its development. Information on the services and support available in the local community will also be provided.

Helpful information

Creative Commons Attribution 3.0 Australia (CC BY 3.0)
Last updated:
30 July 2015

Page feedback

  1. How satisfied are you with your experience today? *