National Institutes of Health Clinical Center – Bethesda

The NIH Clinical Center in Bethesda, Maryland is the world's largest hospital dedicated entirely to clinical research, operating as part of the National Institutes of Health. Since opening in 1953, it has enrolled over 500,000 volunteers in clinical studies.

The Clinical Center does not accept patients seeking routine medical care — instead, it exclusively treats patients enrolled in research protocols. It houses 200 outpatient clinics and 243 inpatient beds, conducting studies across cancer, infectious disease, rare diseases, cardiovascular conditions, and many other areas of medicine.