“Mental retardation” was once an official medical diagnosis, but it is no longer used in any major diagnostic system, federal law, or clinical guideline. The term was formally replaced by “intellectual disability” through a series of changes between 2010 and 2013, and today no mainstream medical organization recognizes “mental retardation” as an accepted clinical label.
How It Became a Medical Term
In the early twentieth century, the clinical language for intellectual disabilities was even harsher than “retardation.” Terms like “feeblemindedness,” “idiocy,” and “mental defect” were standard in medical literature and government policy. “Mental retardation” emerged as a deliberate improvement, a term considered more neutral and scientifically precise than what came before it. By the mid-twentieth century, it had become the dominant diagnosis used in psychiatry, education, and social services across the United States and internationally.
For decades, “mental retardation” appeared in the American Psychiatric Association’s Diagnostic and Statistical Manual (DSM), the World Health Organization’s International Classification of Diseases (ICD), and throughout U.S. federal law. It was a legitimate clinical term with defined diagnostic criteria, not slang.
Why Medicine Dropped the Term
The same pattern that made “mental retardation” necessary in the first place eventually caught up with it. The word “retard” became a common insult, and the clinical term itself took on a stigma that affected the people it was meant to describe. Advocacy groups, families, and clinicians argued that continuing to use it in medical and legal contexts reinforced that stigma.
The shift happened in stages. In October 2010, the U.S. Congress passed Rosa’s Law, named after a nine-year-old girl with Down syndrome from Maryland. The law changed every reference to “mental retardation” in specified federal statutes to “intellectual disability,” and replaced “a mentally retarded individual” with “an individual with an intellectual disability.” Federal agencies, including the Social Security Administration, were required to make matching changes across all of their regulations.
In 2013, the American Psychiatric Association published the DSM-5, which officially replaced “mental retardation” with “intellectual disability (intellectual developmental disorder)” as the diagnostic term. The APA noted this brought its manual into alignment with the World Health Organization, the American Association on Intellectual and Developmental Disabilities, and the U.S. Department of Education. The WHO followed a similar path: its current classification system, the ICD-11, uses “disorders of intellectual development” and has removed the word “retardation” entirely from that category.
What “Intellectual Disability” Actually Means
The updated terminology came with updated diagnostic criteria. Intellectual disability is identified by significant limitations in two areas: cognitive functioning (learning, problem-solving, judgment) and adaptive functioning (communication, social participation, daily living skills). Both limitations must begin during the developmental period, typically before age 18.
Older definitions relied heavily on IQ scores alone. A specific full-scale IQ score is no longer required for diagnosis, though standardized testing remains part of the evaluation. An IQ score of around 70 to 75 suggests a significant limitation in intellectual functioning, but clinicians now also require a score of two or more standard deviations below the population average on a standardized measure of adaptive skills. This means a person’s real-world abilities, not just their performance on an intelligence test, shape the diagnosis.
Where “Retardation” Still Appears in Medicine
While “mental retardation” has been retired as a diagnosis, the word “retardation” itself hasn’t vanished from all medical vocabulary. You may still encounter it in narrower clinical contexts where it simply means “slowing.” “Intrauterine growth retardation” (now more commonly called “fetal growth restriction”) describes a baby growing more slowly than expected during pregnancy. “Psychomotor retardation” refers to a slowing of physical movement and thinking that can occur during severe depression. In these uses, the word functions as a technical descriptor of pace rather than a label for a person or a condition.
That said, even in these contexts, newer terminology is gradually taking over. “Growth restriction” is now preferred in obstetrics guidelines, and many clinicians describe psychomotor slowing without using the word “retardation” at all.
The Broader Pattern
The lifecycle of “mental retardation” as a diagnosis follows a well-documented pattern in medicine. A neutral term is introduced to replace a stigmatized one. Over time, the new term absorbs the same negative associations. Eventually it, too, gets replaced. “Feeblemindedness” gave way to “mental deficiency,” which gave way to “mental retardation,” which gave way to “intellectual disability.” Each change reflected both evolving scientific understanding and a recognition that language shapes how people are treated.
So while “retarded” was once a legitimate medical term, it holds no current standing in clinical practice, federal law, or international diagnostic systems. The recognized term today is “intellectual disability,” and that shift is complete across every major institution that diagnoses or provides services for the condition.