Key keywords: undiagnosed ME/CFS, 10 million undiagnosed Americans, chronic fatigue, brain fog, recurrent headaches, post-viral illness, US public health gap, chronic disease diagnostic access, ME/CFS stigma, post-exertional malaise A new joint report from the U.S. Centers for Disease Control and Prevention (CDC) and national chronic illness advocacy organization Solve ME/CFS Initiative has revealed that an estimated 10 million U.S. residents are living undiagnosed with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), a disabling chronic condition that has long been underrecognized and underresearched by the U.S. medical system. ME/CFS is marked by a cluster of persistent, life-disrupting symptoms: debilitating fatigue that does not improve with rest, cognitive dysfunction commonly referred to as "brain fog" that impairs memory, focus and executive function, frequent severe headaches, muscle and joint pain, and post-exertional malaise – a sharp worsening of all symptoms after even mild physical or mental activity. The report notes that roughly 90% of people living with ME/CFS have not received a formal diagnosis, meaning they are unable to access targeted care, workplace accommodations, or disability benefits that could improve their quality of life. Multiple barriers drive the staggering undiagnosed rate. First, there is no widely available standardized biological test for ME/CFS, so diagnosis relies on patient self-reporting of symptoms and provider knowledge of diagnostic criteria. Surveys cited in the report show that fewer than 30% of primary care providers in the U.S. have received formal training on ME/CFS, leading many to dismiss symptoms as signs of stress, anxiety, depression, or poor lifestyle choices. On average, patients wait between 2 and 5 years to receive a correct diagnosis, with many visiting 5 or more different providers before getting answers. The report also links the recent surge in undiagnosed cases to the COVID-19 pandemic, noting that up to 30% of people with long COVID meet the diagnostic criteria for ME/CFS. Public health experts writing in the report warn that the undiagnosed population represents a hidden public health crisis, with an estimated $36 billion in annual economic losses from missed work and avoidable healthcare costs tied to unaddressed ME/CFS. The report calls for urgent investments in ME/CFS research, expanded provider training, national public awareness campaigns to reduce stigma around the condition, and simplified screening tools for primary care settings to catch cases earlier.