Serious mental illnesses (SMIs) are a small subset of the 300 mental illnesses that are in DSM. While the line between mental health and serious mental illness is debatable, the extremities are clear. Three separate efforts to define serious mental illness have come to similar conclusions and report similar numbers of people have it.

CMHS: The Center for Mental Health Services had to define SMI when it was created in order to distribute mental health block grants to states proportional to the number of SMI in each state. They defined SMI as

mental illnesses listed in DSM that “resulted in functional impairment which substantially interferes with or limits one or more major life activities.” (CMHS 1999, FN *)

To calculate how many adults over eighteen in each state had serious mental illness, CMHS had to define “functional impairment.” After doing so, CMHS noted that “90% [of those meeting the criteria for serious mental illness] either have a severe disorder like schizophrenia or bipolar disorder, or a disorder and work impairment, or a disorder and report being suicidal.”

By all accounts, serious mental illnesses include “schizophrenia-spectrum disorders,” “severe bipolar disorder,” and “severe major depression” as specifically and narrowly defined in DSM. People with those disorders comprise the bulk of those with serious mental illness. However, when other mental illnesses cause significant functional impairment and substantially limit major life activities they also count as a serious mental illness.

NIMH: According to the National Institute of Mental Health, serious mental illness is relatively rare, affecting only 5% of the population over 18. Serious mental illness includes schizophrenia; the subset of major depression called “severe, major depression”; the subset of bipolar disorder classified as “severe” and a few other disorders.

  • Schizophrenia (NIMH defines all schizophrenia as “severe”): 1.1% of the population (FN 1)
  • The subset of bipolar disorder classified as “severe”: 2.2% of the population (FN 2)
  • The subset of major depression called “severe, major depression”: 2.0% of the population (FN 3)

Therefore total “severe” mental illness in adults by diagnosis: 5.3% of the population without accounting for overlap. (FN 4) SAMHSA puts the rate at 4%.

National Advisory Mental Health Council: A separate major effort to define serious mental illness and calculate its prevalence took place in 1993 when the Senate Committee on Appropriations asked that the National Advisory Mental Health Council report on how much it would cost to provide insurance coverage for people with “severe mental illness” commensurate with the coverage of other illnesses. It stated “severe mental illness is defined through diagnosis, disability, and duration, and includes disorders with psychotic symptoms such as schizophrenia, schizoaffective disorder, manic depressive disorder, autism, as well as severe forms of other disorders such as major depression, panic disorder, and obsessive compulsive disorder.It came to similar conclusions as CMHS. Using that definition they found  3% of adults have severe mental illness, an estimate very close to what CMHS and NIMH found.

US mental health spending and mental health non-profits focus almost exclusively on people who do not have serious mental illness, rather than those who do. This is the single major problem with the US mental health system. More money will not help the seriously mentally ill if it is not allocated to the seriously ill. Prioritization is needed.

We should replace mission creep with mission control and return the mental health system to one that gets treatment to those with the most serious mental illness rather than one that works to improve the mental health of all others.

NOTE: The complete explanation of serious mental illness and what is wrong with our system can be found in Appendix A of “Insane Consequences: How the Mental Health Industry Fails the Mentally Ill,”  (Prometheus, 2017) available on Amazon and Barnes & Noble in hardcover and ebook.

Following are the footnotes

(9/2017 Update: URLS may no longer work and the estimates may have changed since this document was originally created.)

FN *: The definition derives from two steps included in the legislation creating SAMHSA and requiring it to distribute mental health block grants to states proportional to the number of persons with serious mental illness in each state. As the first step, Congress required CMHS to define “serious mental illness in adults.” ADAMHA Reorganization Act of 1991, Pub. L. 102-321, Pub. L. 102-321 (1992), pp. 323–442, (accessed July 17, 2016). The second step, after it was defined, was to estimate its prevalence in each state.

(1) NIMH classifies all Schizophrenia as severe. “Schizophrenia is a chronic, severe, and disabling mental disorder characterized by deficits in thought processes, perceptions, and emotional responsiveness.

(2) NIMH “Bipolar Disorder Among Adults” “2.2% of U.S. adult population are classified as “severe”. See note below under “major depressive disorder” to see how severity was defined.

(3) Major Depressive Disorder Among Adults” NIMH notes that 6.7% of adults have major depression and 30.4% of those (2.0% of U.S. Population) is classified as “severe”, quoting Kessler RC, Chiu WT, Demler O, Walters EE. Prevalence, severity, and comorbidity of twelve-month DSM-IV disorders in the National Comorbidity Survey Replication (NCS-R). Archives of General Psychiatry, 2005 Jun;62(6):617-27. To be classified as ‘severe’ in addition to meeting DSM criteria, the disorder had to meet the following criteria. “Twelve-month cases were classified as serious if they had any of the following: a 12-month suicide attempt with serious lethality intent; work disability or substantial limitation due to a mental or substance disorder; positive screen results for non- affective psychosis; bipolar I or II disorder; substance depen- dence with serious role impairment (as defined by disorder- specific impairment questions); an impulse control disorder with repeated serious violence; or any disorder that resulted in 30 or more days out of role in the year.” The study is available at

(4) “Prevalence of Serious Mental Illness Among U.S. Adults by Age, Sex, and Race in 2008 (NSDUH)” at

DJ Jaffe is Executive Director of the non-partisan Mental Illness Policy Org., and author of Insane Consequences: How the Mental Health Industry Fails the Mentally Ill. He is a critic of the mental health industry for ignoring the seriously ill, and has been advocating for better treatment for individuals with serious mental illness for over 30 years. He has written op-eds on the intersection of mental health and criminal justice policy for the New York Times, Wall St. Journal and the Washington Post. New York Magazine has credited him with being the driving force behind the passage of New York’s Kendra’s Law and Congress incorporated ideas proposed by DJ in the Helping Families in Mental Health Crisis Act.