5 million Americans aged 18 and older Up to 90 percent WomensHealth.gov, almost exclusively Fibromyalgia Fact Sheet – WomensHealth.gov reports 4 million Americans three months Up to 90 percent 5 million Fibromyalgia U.S. Department of Health and Human Services Department of Health and Human Services. up to 90 percent Women’s Health U.S. Department of Health and Human Services