A thorough medical history, physical examination, mental status examination, and laboratory tests must be conducted to identify underlying or contributing conditions that require treatment. Diagnosis or classification cannot be made without such an evaluation.

Clinically evaluated, unexplained chronic fatigue cases can be classified as CFS if the patient meets the following criteria:

1. Clinically evaluated, unexplained persistent or relapsing chronic fatigue that is of new or definite onset (ie. not lifelong) and is not the result of ongoing exertion; is not substantially alleviated by rest, and results in substantial reduction in previous levels of occupational, educational, social, or personal activities.

2. The concurrence of four or more of the following symptoms:
   • Substantial impairment in short term memory or concentration
   • Sore throat
   • Tender lymph nodes
   • Muscle pain
   • Multi-joint pain without swelling or redness
   • Headaches of a new type, patter, or severity
   • Unrefreshing sleep
   • Post exertional malaise lasting more than 24 hours

These symptoms must have persisted or recurred for 6 or more consecutive months of illness and must not have predated the fatigue.

The CDC publication, dated December 15, 1994, is entitled:

The Annals of Internal Medicine; Vol. 121, No. 12, Pg. 953-959
The Chronic Fatigue Syndrome: A Comprehensive Approach to Its Definition and Study

The study was authored by:

Keiji Fukuda, M.D., M.P.H.
Stephen Straus, M.D.
Ian Hickey, M.D., FRANZCP
Michael C. Sharpe, M.R.C.P., M.R.C. Psych.
James G. Dobbins, Ph.D.
Anthony Komaroff, M.D.
And The International Chronic Fatigue Syndrome Study Group