Dr. Byron Hyde, a very experienced researcher, sees ME as always being sudden onset and CFS being a catch-all name only, which covers many other possible conditions.He is not the only doctor or researcher who thinks this way, is my impression. Yet, the best definitions we have, the CCC and ICD, still say sudden or gradual onset. Here is a hypothesis I have which might explain at least part of this discrepancy: Children who get ME are known to have better recovery, in general, than adults. Some even seem to recover fully. Some claim they have, but on closer examination, according to Dr. David Bell, really have not, but have integrated ways of coping so well--rest, careful diet, etc.--that they seem to be doing better than they are. Nevertheless, young, more resilient bodies do seem more capable of apparent recovery. What I wonder is if, for those infants or children who got ME and were probably were never correctly diagnosed, then went on to apparent recoveries, could it not be that later on in life, with further stresses, illnesses, or just normal aging, the original ME then rears its head again? This is what is known to happen with Polio, and ME as at least sometimes the result of those same enteroviruses responsible for Paralytic Polio. I think this pattern of apparent recovery then later recurrence might explain some of the gradual onset cases. The body never did heal completely but only mounted a successful defense and many compensations, which, after decades perhaps, have been eroded. I think this is what happened to me. I wanted to present this as a hypothesis which might account for gradual onset. And/or if, ME/CFS (using the whole, current designation) turns out to be an autoimmune illness, aren't these known to develop at different rates in different individuals too?