I didn't know about this study until now, but this is a paper from the Statistics Canada Health reports publication: http://statcan.gc.ca/pub/82-003-x/2006001/article/sympt/82-003-x2006002-eng.pdf This is part of the results of the 2003 Canadian Community Health survey, which had 135,573 respondents, (household response rate of 80.6%) and covered anyone over 12 in each household. All health conditions were self-reported only. The prevalence was 1.3% for CFS, 1.5% for FMS and 2.4% for MCS. 36% of people reporting CFS also had depression. (further discussed here: http://fampra.oxfordjournals.org/content/25/6/414.full - I've just skimmed it, but variables such as financial strain were strong predictors). In comparison, the rate of depression for MS patients in an earlier Canadian survey was 25.7% for those in the 18 to 45 year old range. http://www.ncbi.nlm.nih.gov/pubmed/14663036 Note that even if the remaining 19.4% who did not respond were included and assumed not to be have CFS, the lower bound on the prevalence would still be somewhere around 1%.