A recent article by in this journal by Jason, Najar, Porter, and Reh, “Evaluating the Centers for Disease Control’s Empirical Chronic Fatigue Syndrome Case Definition”

(2009) attempted to critically explore several pertinent issues concerning diagnosing chronic fatigue syndrome (CFS). Most of these issues have been brewing since inter-national adoption of the 1994 CFS case definition by Fukuda, Straus, Hickie, Sharpe, Donnibs, and Komaroff (1994), and it is high time to address them in a peer-reviewed and public forum. The 1994 CFS case definition (Fukuda et al., 1994) remains the international standard for diagnosing the illness. It captures the key domains of CFS, is user friendly, is intuitive, can be administered in a few minutes of conversation with no survey instruments or equipment, and works well in clinical settings. Unfortu-nately, the 1994 CFS case definition suffers from lack of standardization, which contributes to irreproducibility and instability in diagnosis between (and within) specific research settings. This led the Centers for Disease Control and Prevention (CDC) to form the International Chronic Fatigue Syndrome Study Group, which included 35 scien-tists, clinicians, and patient advocates from around the world. The Group included Jason and authors of all previ-ously published CFS case definitions and met over 3 years to consider ambiguities in the 1994 case definition. In 2003, the Group published its consensus as to ambiguities and recommendations for resolving them (Reeves et al., 2003). In brief, the Group agreed that the 1994 diagnostic construct of CFS was valid and recommended that major dimensions of the illness (functional impairment, fatigue, and the eight defining symptoms) be measured by means of internationally standardized and validated instruments and that medical and psychiatric conditions with similar clinical presentations be evaluated by current evidence-based means