Module 12: Mental Retardation (Intellectual Disability)

Intellectually Disabled Child PlayingIntellectual Disability

Diagnostic code: 317, 318.x
Information below is from DSM-PC. Refer to DSM-PC and DSM-5/DSM-IV-TR for full psychiatric criteria and further description.

Intellectual disability presents differently in infancy, early childhood, middle childhood, and adolescence. The following are examples of how MR may be manifested across developmental periods.

Description of Symptoms


  • Significant limitations in emotional expressiveness, language, purposeful behavior, gross and fine motor skills, and apparent cognitive abilities
  • Mild and moderate deficits may go undetected

Early Childhood

  • Significant delays in communicating, walking, self feeding, toilet learning, and social interaction
  • Intellectual function is significantly below average

Middle Childhood and Adolescence

  • Developmental delays are usually clear by this age
  • Evaluation can identify strengths and weaknesses in cognitive and adaptive abilities
Diagnosis and Coding

The diagnosis of intellectual disability

Borderline intellectual functioning (IQ level 71 to 84)
Diagnostic code: V62.89

Mild MR (IQ level 50 to 55 to approximately 70)
Diagnostic code: 317

In about 85 percent of individuals with MR, the level of retardation is classified as mild. MR is best detected in infancy or early childhood so that early intervention strategies can be initiated; however, mild MR may not be recognized until the child enters preschool or elementary school. Individuals with mild MR can typically achieve at least fourth-grade- level to sixth-grade-level scholastic skills, and they can graduate from high school. As adults, they can hold jobs in the regular work force, marry, and raise families. If they encounter challenging life problems, they may need intermittent environmental supports.

Moderate MR (IQ level 35 to 40 to 50 to 55)
Diagnostic code: 318

In about 10 percent of individuals with MR, the level of retardation is classified as moderate. Moderate MR is usually identified during infancy or early childhood. School-age children with moderate MR frequently benefit from special education programs. With limited but consistent environmental supports, adults with moderate MR can thrive in neighborhoods and communities. Some function well in regular jobs, while others need more supportive job settings.

Severe MR (IQ level 20 to 25 to 35 to 40)
Diagnostic code: 318.1

In about 3 to 4 percent of individuals with MR, the level of retardation is classified as severe. These individuals frequently have motor and neurological impairments as well as significant problems communicating. People with severe MR need extensive environmental supports and individualized help to maximize their adaptive skills. They can participate in their self-care. As adults, they may be able to work productively in structured work environments.

Profound MR (IQ level below 20 or 25)
Diagnostic code: 318.2

In 1 to 2 percent of individuals with MR, the level of retardation is classified as profound. These individuals also have pervasive problems in sensorimotor (both sensory and motor) and communicative functioning. Most children and adolescents with profound MR need pervasive or multiple environmental supports, including supports for self-care tasks such as grooming, toileting, and eating.

MR severity unspecified
Diagnostic code: 319

Diagnosed when there is a strong presumption of mental retardation but the child’s intelligence is untestable by standard intelligence tests.


  1. American Psychiatric Association. (2000). Diagnostic and Statistical Manual of Mental Disorders (4th ed.). Washington, D.C.: American Psychiatric Association.

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