This is a subject that has been raised a lot, so I thought it might be good to have a thread. I only recently started looking into it a bit further than the basic diagnostic criteria. see https://www.s4me.info/threads/main-diagnostic-criteria-and-guidelines.189/ The actual "Report of a consensus meeting held at Green College,Oxford 23 March 1990" ie A report--chronic fatigue syndrome: guidelines for research. Sharpe MC, Archard LC, Banatvala JE, Borysiewicz LK, Clare AW, David A, Edwards RH, Hawton KE, Lambert HP, Lane RJ, et al J R Soc Med. 1991 Link to article raises a lot of questions. A few things (apart from the obvious omission of PEM, and the contributors including Sharpe, Wessely and White) " Aims: The aim of the meeting was to seek agreement amongst research workers on recommendations for the conduct and reporting of future studies of patients with chronic fatigue." " Chronic fatigue syndrome(CFS) (a)A syndrome characterized by fatigue as the principal symptom. (b)A syndrome of definite onset that is not life long." The introduction of PIFS (post-infectious fatigue syndrome): " In reporting studies it should be clearly stated which of these two syndromes is being studied. " (Is PIFS included anywhere else as a subtype of CFS?) I have tried to find studies that specify they are on PIFs but have only found this one surprisingly from last year (I think there is a thread on it) : http://www.meresearch.org.uk/news/experiences-of-pifs/ http://www.meresearch.org.uk/news/the-real-experience-of-fatigue/ and this https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4662830/ Need to go and read some more (I think Keith Geraghty has been looking at this issue(?)).