ABSTRACT
Accurate diagnosis of Chronic Fatigue Syndrome (CFS) is greatly complicated by the vague wording of many of the major diagnostic criteria (i.e., substantial reductions in previous levels of occupational, educational, social, or personal activities) and the absence of guidelines for health care professionals to follow. The lack of operationally explicit criteria has forced health care professionals to rely heavily on their own clinical judgement, which may be biased by personal and highly idiosyncratic factors. Thus, in the case of CFS, the lack of consensus among clinicians regarding the interpretation and application of the diagnostic criteria has likely produced problems in diagnostic reliability. Data from a recent community based epidemio-logic study are presented to illustrate these problems and provide recommendations for improving criterion reliability.