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Nationwide Ambulatory Surgery Sample (NASS)

Nationwide Ambulatory Surgery Sample (NASS)

What is the NASS?

The Nationwide Ambulatory Surgery Sample (NASS) is part of the family of databases and software tools developed for the Healthcare Cost and Utilization Project (HCUP). The NASS produces national estimates of major ambulatory surgery encounters performed in hospital-owned facilities across the country. It contains clinical and resource-use information that is included in a typical hospital-owned facility record, including patient characteristics, clinical diagnostic and surgical procedure codes, disposition of patient, total charges, expected source of payment, and facility characteristics.

Advance Your Research

Apply valuable clinical and nonclinical variables to your research, including—
  • Current Procedural Terminology (CPT®) procedures codes for encounters with at least one in-scope major ambulatory surgery
  • Patient demographic characteristics such as age, sex, and urban-rural designation of residence
  • Expected payment source
  • Total charges
  • Hospital characteristics such as region, bed size, teaching status, and ownership
Address Critical Topics

Rely on the NASS to study national ambulatory surgery encounters, including:
  • Trends in major ambulatory surgery encounters
  • Charges for select ambulatory surgery services
  • Quality of ambulatory surgery care
  • Impact of health policy changes
  • Access to major ambulatory surgery care
  • Utilization of select ambulatory surgery services by special populations
A Comprehensive, User-Friendly Resource

The NASS provides national estimates for approximately 10 million ambulatory surgery encounters and more than 13 million ambulatory procedures in the United States, making it an exceptional resource for conducting research on major ambulatory surgeries. For the NASS, major ambulatory surgeries are defined as selected invasive, therapeutic surgical procedures that typically require the use of an operating room and regional anesthesia, general anesthesia, or sedation. Available annually starting in the 2016 data year, NASS data are standardized across years to facilitate ease of use.

Expand Your Analyses
  • Use HCUP tools. Free tools and software are available to estimate hospital costs, assess quality of care, and identify comorbidities. Most tools also can be used with other administrative healthcare databases.
  • Make the most of your research. HCUP Supplemental Files enhance applicable HCUP databases with additional data elements or analytically useful information. They cannot be used with other administrative databases.
  • Learn more about NASS data. Publications using the NASS, database documentation, and associated reports can be found on HCUP-US (
Easy to Purchase

HCUP's Nationwide Databases are available for purchase from the online HCUP Central Distributor:

The HCUP Central Distributor is the entity that accepts, processes, and fulfills applications for the purchase and use of HCUP databases.

The NASS is provided in CSV format via secure digital download from the online HCUP Central Distributor. A statistical software package, such as SAS®, SPSS®, or Stata®, is required for analysis. Programs to load data into software packages are provided.

For a list of prices (including discounted student rates) and complete purchasing information, visit the HCUP-US website: This site also provides detailed information about the Data Use Agreement, data elements, and software tools.

The Healthcare Cost and Utilization Project (HCUP, pronounced "H-Cup") is a family of powerful health care databases, software tools, and products for advancing research. Sponsored by the Agency for Healthcare Research and Quality (AHRQ), HCUP includes the largest all-payer, encounter-level collection of longitudinal health care data (inpatient, ambulatory surgery, and emergency department) in the United States, beginning in 1988.

HCUP is a Federal-State-Industry Partnership that brings together the data collection efforts of many organizations — such as State data organizations, hospital associations, private data organizations, and the Federal Government — to create a national information resource. HCUP would not be possible without the contributions of data collection Partners from across the nation.

For more information about HCUP, please visit

Internet Citation: Nationwide Ambulatory Surgery Sample (NASS). Healthcare Cost and Utilization Project (HCUP). March 2020. Agency for Healthcare Research and Quality, Rockville, MD.
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Last modified 3/19/20