Bedsize categories are based on hospital beds, and are specific to the hospital's location and teaching status. Bedsize assesses the number of short-term acute care beds set up and staffed in a hospital. Hospital information was obtained from the AHA Annual Survey of Hospitals.

Beginning in 2000, the hospital's bedsize categories are defined using region of the U.S., the urban-rural designation of the hospital, in addition to the teaching status. Rural hospitals were not split according to teaching status, because rural teaching hospitals were rare. A hospital is considered to be a teaching hospital if it has an AMA-approved residency program, is a member of the Council of Teaching Hospitals (COTH) or has a ratio of full-time equivalent interns and residents to beds of .25 or higher. The classification of a hospital location as urban or rural has changed over time. Prior to 2006 data, the urban/rural designation was based on Metropolitan Statistical Areas (MSA). Beginning with the 2006 data, this designation was determined by the Core Based Statistical Area (CBSA). This change in 2006 contributed to a slight decline in the number of hospitals that were classified as rural and a corresponding increase in the number of hospitals that were classified as urban.

Prior to 2000, the bedsize category did not vary by region and teaching hospitals were defined as having an AMA approved residency program or having membership in the Council of Teaching Hospitals.

HOSP_BEDSIZE is missing if the data source that contributed discharge data to the NIS prohibits the release of hospital identifiers.