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The National Death Index (NDI) is a centralized database of U.S. death record information maintained by the National Center for Health Statistics (NCHS), part of the Centers for Disease Control and Prevention (CDC). NCHS worked with states to establish it, and states submit death certificate data through the Vital Statistics Cooperative Program. In cohort studies and follow-up research across public health, the NDI lets approved researchers find out whether study participants have died, and where and when.
What it is
The NDI is available solely to researchers who use it for statistical purposes in public health and medical studies. It is not available for personal, legal, administrative, or genealogical use. Researchers must first be approved by an independent advisory board.
There are two levels of search:
- NDI: returns the state of death, the date of death, and the death certificate number for matched records.
- NDI Plus: adds the cause or causes of death. Its base service charges are higher than those of the standard search.
Who runs it and what it covers
NCHS administers the NDI, and it is fully funded by user fees. A fee consists of a base service charge plus a per-record fee that depends on the search type; current amounts are published on the NDI costs and payments page of the CDC site.
The index holds death records from 1979 onward for the 50 states, the District of Columbia, New York City, Puerto Rico, and the U.S. Virgin Islands, plus out-of-country deaths of U.S. military personnel since 1979. Guam, American Samoa, and the Northern Mariana Islands have records for select years only. CDC describes the file as holding more than 115 million death records. The final annual file becomes available 12 or more months after year-end, and an Early Release Program makes preliminary records available sooner and later converts them to final.
NCHS also uses the index for its own data linkage work. The linked mortality files connect National Health and Nutrition Examination Survey (NHANES) participants to NDI records. The NHANES linked mortality files cover NHANES 1999-2018 and NHANES III, with mortality follow-up through December 31, 2022 in the restricted-use release. The public-use file contains a limited set of mortality data for adults, and some information was altered to protect identities: for certain records, follow-up time or underlying cause of death was replaced with synthetic values, while alive or deceased status was not changed. It can be downloaded freely, with data dictionaries and sample SAS, Stata, and R programs. The restricted-use file includes adults and children, is unaltered, and is available only through the NCHS Research Data Center (RDC) network for approved projects. The two versions cannot be used together in the RDC.
How to apply
CDC takes NDI applications through its NDI Portal and describes the following elements of the process.
- Eligibility and approval: The applicant must be a researcher using the data for statistical purposes and must be approved by an independent advisory board. For repeated searches, applicants upload their most current IRB approval letter, if applicable.
- Data governance: Projects that handle identifiable participant data usually pair the application with institutional paperwork such as a data use agreement template or a signed data use agreement. See also the comparison of a certificate of confidentiality and a data use agreement.
- Prepare records: Each submitted record must meet at least one of three combinations of identifiers:
- first and last name plus Social Security Number;
- first and last name plus month and year of birth; or
- Social Security Number plus date of birth plus sex.
- Submit files: Files can be sent through CDC’s secure File Transfer Protocol (sFTP) site. Files must be password-protected using self-decrypting software, and each file needs its own NDI Transmittal Form along with a Worksheet for Calculating NDI Charges.
- Receive results: NDI staff usually return the encrypted search results and the original data files within two weeks of file submission.
Strengths and limits
Strengths
- National reach: It covers all 50 states, the District of Columbia, and several territories, so a death is found even if a participant moved between states.
- Cause of death: NDI Plus adds cause or causes of death, which cause-specific analyses and a NIH project narrative public health relevance statement can draw on.
Limits
- File lag: The final annual file is available 12 or more months after year-end.
- Identifier requirements: Records need one of the three minimum identifier combinations above.
- Restricted use: It cannot be used for personal, legal, administrative, or genealogical purposes, and applicants need advisory board approval.
Reporting of cohort studies that use NDI linkage can follow the STROBE checklist.
Alternatives
Which source fits depends on the cohort, budget, and variables needed. This table describes what each CDC resource is, using only facts from the CDC pages listed in the sources.
| Resource | Operator | Cause of death | Access |
|---|---|---|---|
| NDI | CDC / NCHS | No (state, date, certificate number) | Approved researchers; user fees |
| NDI Plus | CDC / NCHS | Yes | Approved researchers; higher base service charges |
| NHANES public-use linked mortality file | CDC / NCHS | Limited; some values synthetic | Free download |
| NHANES restricted-use linked mortality file | CDC / NCHS | Yes; unaltered | Research Data Center, approved projects |
FAQ
What is the difference between standard NDI and NDI Plus?
The standard NDI returns the state of death, date of death, and death certificate number. NDI Plus adds the cause or causes of death and has higher base service charges.
Who is eligible to use National Death Index data?
Researchers using the data for statistical purposes in public health and medical studies, approved by an independent advisory board. It is not available for personal, legal, administrative, or genealogical use.
What are the NHANES linked mortality files?
NCHS links NHANES participants to NDI records. A public-use version is freely downloadable with some values altered, and an unaltered restricted-use version is available through the NCHS Research Data Center for approved projects.
What minimum participant information is needed to query the NDI?
One of three combinations: first and last name plus Social Security Number; first and last name plus month and year of birth; or Social Security Number plus date of birth plus sex.
How long does a search take?
NDI staff usually return encrypted results within two weeks of file submission, according to CDC.
Sources
Checked 2026-11-07.
- CDC, NCHS. National Death Index. https://www.cdc.gov/nchs/ndi/index.html
- CDC, NCHS. NDI eligibility requirements. https://www.cdc.gov/nchs/ndi/eligibility/index.html
- CDC, NCHS. Applying for NDI searches. https://www.cdc.gov/nchs/ndi/apply/index.html
- CDC, NCHS. Data Linkage: Mortality files. https://www.cdc.gov/nchs/data-linkage/mortality.htm
