How long does CFS last?

There are very few published studies which have documented the natural history of CFS. The illness can have a spectrum of possible outcomes, ranging from a relatively mild illness lasting just six months, to a severe illness lasting for many years. The consensus amongst researchers seems to be that most people improve over time, although the percentage of people who regain their pre-illness level of health is unknown. Based on the epidemiological study conducted in the Richmond Valley, 'full-blown' CFS lasts for more than five years in 33% of people.

In a recent study published in the British Medical Journal, 103 CFS patients who had already been ill for several years were followed up for an average period of three years. At the end of the study, only six out of 103 patients had recovered completely.