CDC WONDER is the CDC's free public query system for US mortality data, birth records, population estimates, and disease surveillance. No login, no API key, no cost.
The interface looks like it shipped in 1998 (because it did). But the underlying data powers most published research on US death rates, drug overdoses, and maternal mortality. If you need authoritative national health statistics, this is where they live.
What CDC WONDER actually is
CDC WONDER (Wide-ranging ONline Data for Epidemiologic Research) covers eight major dataset categories. Unlike openFDA's REST API, WONDER is primarily a web-based query tool. You submit form-based queries and receive tabulated results. The tradeoff: authoritative data, clunky access.
Key datasets available
| Dataset | Coverage | Updated |
|---|---|---|
| Underlying Cause of Death | 1999-2024 | Annually |
| Multiple Cause of Death | 1999-2024 | Annually |
| Natality (birth data) | 2016-2023 | Annually |
| Infant Deaths | 2007-2022 | Annually |
| Population Estimates | 1990-2023 | Annually |
| Sexually Transmitted Infections | 2000-2022 | Annually |
| Vaccine Adverse Events (VAERS) | 1990-present | Weekly |
| COVID-19 Provisional Deaths | 2020-present | Weekly |
Mortality data: the flagship dataset
The most-used WONDER dataset is the mortality file. It provides counts and rates of deaths by:
- Cause of death (ICD-10 codes)
- Demographics (age, sex, race, ethnicity)
- Geography (state, county, census region)
- Year and month
For example, you can query: "How many opioid-related deaths occurred in Ohio in 2023, broken down by age group?" WONDER answers that directly.
How to query WONDER
The primary interface is web-based at wonder.cdc.gov. For each dataset, you:
- Select the dataset from the main menu
- Set grouping variables (how you want results organized)
- Set filter criteria (location, time period, demographics)
- Choose specific cause-of-death codes if applicable
- Submit and receive a results table
Results can be exported as tab-delimited text files for analysis.
Programmatic access limitations
WONDER was built before REST APIs became standard. Programmatic access is limited:
- No official REST API for most datasets
- SODA API exists for some CDC datasets at data.cdc.gov (separate system)
- Bulk downloads available for some datasets in compressed text format
- Automated queries possible through HTTP POST to the WONDER forms, but fragile
The CDC SODA (Socrata Open Data Access) endpoint at data.cdc.gov provides API access to some datasets that overlap with WONDER, but not all of them. We cover the differences in detail in our CDC WONDER vs data.cdc.gov comparison.
SODA API for CDC data
For datasets available through data.cdc.gov, the SODA API is the developer-friendly option:
# Weekly COVID-19 death counts by state
curl "https://data.cdc.gov/resource/r8kw-7aab.json?$limit=10&$where=state='California'"
SODA supports filtering, pagination, aggregation, and JSON/CSV output formats. Rate limits are 1,000 requests per hour without a token, higher with a free app token.
Use cases for health data developers
Drug overdose surveillance: WONDER mortality data coded with ICD-10 codes T36-T50 (poisoning by drugs) enables time-series analysis of overdose trends by substance, geography, and demographics.
Maternal mortality research: Natality and mortality files combined allow analysis of maternal death rates by hospital type, insurance status, and geographic access to care.
Vaccine safety monitoring: VAERS data in WONDER complements the openFDA VAERS endpoint, providing a different query interface over the same underlying data.
Environmental health: The environmental dataset links health outcomes to specific geographic exposures, useful for health equity research.
Data quality considerations
WONDER data has specific limitations to account for:
- Suppressed cells: Any count between 1-9 is suppressed to protect privacy. This makes county-level analysis difficult for rare conditions.
- Provisional data: Recent years may show lower counts because death certificates take time to process. The CDC flags which years are provisional.
- Coding changes: ICD-10 replaced ICD-9 in 1999. Trend analysis across this boundary requires crosswalk tables.
- Race/ethnicity misclassification: Death certificates rely on funeral director observation, leading to undercounting for American Indian/Alaska Native and Asian populations.
FAQ
Is CDC WONDER free to use? Completely free, no registration required. The data is public domain.
How current is the mortality data? Typically 12-18 months behind. The 2024 data usually becomes available in mid-2026. Provisional data is available faster for COVID-19 and drug overdose deaths.
Can I get individual-level records? No. WONDER only provides aggregate counts and rates. Individual death certificate data requires a research agreement with NCHS.
What is the difference between WONDER and data.cdc.gov? WONDER is the older query system with more historical data. data.cdc.gov is the newer open data portal with API access. Some datasets appear in both, but the collections are not identical. See our full comparison of CDC WONDER vs data.cdc.gov for a detailed breakdown of which to use for what.
How do I cite WONDER data? The CDC provides a suggested citation on each query result page. Include the dataset name, query parameters, and date accessed.
Last verified August 2026.
Related guides
- CDC WONDER vs data.cdc.gov: which one do you need? — detailed comparison of query capabilities, API access, and dataset coverage
- Health Data APIs Compared: openFDA vs CDC SODA vs CMS — if you need API access, CDC's SODA endpoint is one of three major options
- 5 Free US Health Data Sources for Developers — CDC is one of five key federal data systems
- Medicare Drug Spending 2024: Top 10 Drugs Cost $60B+ — federal health data powering real spending analysis
- NPI Registry API: Provider Lookup Guide — another key federal health data endpoint for developers
Published on 2026-08-08 · 5 min read
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