The Primary U.S. Case Definition

The major case definitions and diagnostic criteria for the Chronic Fatigue Syndrome (CFS) were developed from clinical experience and medical research over the past two decades in the United States, Canada, Australia and Europe.

In the United States, the case definition in most widespread use in 2009 was developed in 1994 under the auspices of the U.S. Centers for Disease Control & Prevention (CDC), the primary federal public health agency. The Criteria were published as an article, "The Chronic Fatigue Syndrome: A Comprehensive Approach to its Definition and Study" in 1994 in the Annals of Internal Medicine, a prestigious medical journal. This definition identified the illness as "Chronic Fatigue Syndrome"—the name the CDC gave to the illness in its first CFS definition in 1988. (Hence the 1994 criteria are termed the "revised" definition.)

The definition remains the "official" and "authoritative" definition of the U.S. public health and research agencies and is the one most widely distributed among and subscribed to by many researchers and clinicians in the U.S. and other countries.

The CDC diagnostic criteria are also the standards used by the U.S. Social Security Administration (SSA) in determining CFS/CFIDS/ME disability.

To date, in our opinion the 2003 Canadian Definition is the most medically accurate and detailed case definition available to physicians and patients. A patient and his/her physician will best determine presence of the illness using the Canadian Diagnostic Criteria. So we suggest the 2006 CDC Guidelines (an abridgement of the 1994 case definition) below not be used as the sole method of diagnosing a case of the Chronic Fatigue Syndrome/Chronic Fatigue and Immune Dysfunction Syndrome/Myalgic Encephalopathy/Myalgic Encephalomyelitis (CFS/CFIDS/ME).