12 Million Americans Misdiagnosed Every Year as Diagnostic Errors Cost $870 Billion

A new study from The Schiller Kessler Group finds that medical misdiagnosis is a systemic failure in American healthcare, not a series of isolated mistakes. Based on Johns Hopkins Medicine estimates, roughly 12 million American adults are misdiagnosed every year, close to 3.5% of the U.S. population. Each year about 795,000 Americans suffer serious harm from diagnostic errors: 424,000 are left permanently disabled and 371,000 die. Diagnostic errors and the treatment and corrective care that follow account for an estimated 17.5% of total U.S. healthcare spending, or about $870 billion a year. A 2024 Johns Hopkins analysis found that women and racial or ethnic minorities are up to 30% more likely than White men to be misdiagnosed.

Chronic and autoimmune conditions have some of the highest misdiagnosis rates and the longest delays. Endometriosis, which affects about 1 in 10 women of reproductive age, is misdiagnosed in 75% of cases, usually as IBS, ovarian cysts, or appendicitis, and patients wait an average of 11 years for the right diagnosis, the longest delay in the study. Black women are 50% less likely than White women to be correctly diagnosed. Fibromyalgia has a 50% misdiagnosis rate and affects 4.2% of women compared with 1.4% of men, and patients see an average of 3.7 physicians over 2.3 years before getting an answer. Lupus is misdiagnosed in 46.5% of cases, most often as fibromyalgia or rheumatoid arthritis, and the average diagnostic delay runs past six years. Black women develop lupus at roughly three times the rate of White women, about six years earlier, and more often progress to kidney failure. Lyme disease, diagnosed about 475,000 times a year, has a misdiagnosis rate of 30% to 50%, while celiac disease, which affects about 1 in 133 Americans, is mistaken for IBS in around 25% of cases.

Mental health and neurological conditions carry a different kind of danger, because a wrong diagnosis can create new risks instead of just delaying treatment. Bipolar disorder affects around 5.7 million American adults and has the second highest misdiagnosis rate in the study at 69%, most often mistaken for major depression. That distinction matters because antidepressants can trigger mania in up to 70% of bipolar patients who are misdiagnosed with ordinary depression, and more than a third of patients go 10 years or more without the right diagnosis. Black patients are up to 4 times more likely to be misdiagnosed with schizophrenia. Multiple sclerosis is misdiagnosed in about 18% of cases, usually as migraine. Diagnostic delays have dropped from 4.2 years in the early 2000s to 1.1 years in 2025, but 40.4% of patients still report an initial misdiagnosis. At diagnosis, 38.3% of Black MS patients already have vision loss, compared with 28.6% of White patients.

For acute, time-sensitive conditions, delays are measured in hours and days, not years, but they can be just as deadly. Stroke is misdiagnosed in about 17% of cases and is often mistaken for migraine or vertigo. Up to 12.7% of patients later hospitalized for stroke had already been sent home from an ER. Early stroke identification was missed in 34.9% of cases among Black patients compared with 31.4% among White patients. Women have up to a 59% higher chance of heart attack misdiagnosis than men, and women under 55 are seven times more likely than men to be sent home from the ER without proper cardiac testing. Lung cancer symptoms are mistaken for pneumonia or bronchitis in 25% of cases. That delay is costly, because five-year survival is roughly 60% to 65% when lung cancer is caught early and just 12% at stage four.

The study also links misdiagnosis to medication harm. Nearly a third of outpatient antibiotic prescriptions, about 47 million a year, treat infections that are not bacterial. That overuse fuels C. difficile, which causes up to 250,000 hospitalizations and 14,000 deaths a year. Nearly 1 in 10 patients who take opioids for chronic pain develop dependence or opioid use disorder, and around 9 in 10 patients who take corticosteroids for more than two months develop adverse reactions. Adverse drug reactions lead to about 700,000 emergency visits and 100,000 hospital admissions every year, yet more than 94% go unreported.

The psychological toll is just as clear. “Medical gaslighting” ranked as the number one patient safety concern in ECRI’s 2025 report. In a HealthCentral reader survey, more than 94% of respondents said a doctor had dismissed their concerns, 55% said their condition got worse as a result, and 28% said the delay led to a health emergency. Among patients eventually diagnosed with autoimmune disease, more than 80% said their misdiagnosis damaged their self-worth. Across every category, the study points to one recurring driver: premature closure, settling on the first plausible explanation instead of ruling out alternatives, which contributes to an estimated 47% of diagnostic errors.