1. Clinically evaluated, unexplained, persistent, or relapsing chronic fatigue that is of new or definite onset (has not been lifelong): 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. Concurrent occurrence of four or more of the following symptoms, all of which must have persisted or recurred during six or more consecutive months of illness and must not have predated the fatigue:
A. Self-reported impairment in short term memory
B. Sore throat
C. Tender cervical or axillary lymph nodes
D. Muscle pain
E. Multijoint pain without joint swelling or redness
F. Headaches of a new type, pattern, or severity
G. Non refreshing sleep
H. Postexertional malaise lasting more that twenty-four hours
Problem with the definition is that it is a research definition and excludes many people with the syndrome.