Hospital Service Area File

Market and Geography

Where a hospital's patients come from — and what that reveals about market reach, concentration, and competition.

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What is the Hospital Service Area File

Patient origin, mapped to the ZIP code.

The Hospital Service Area (HSA) file is published annually by CMS and answers a deceptively simple question: where do a hospital's Medicare patients live? For every hospital in the country, it records how many inpatient cases came from each ZIP code of patient residence — along with total charges and total days of care for those patients.

That single structure — one row per hospital per ZIP per year — is what makes geographic market analysis possible. Stack enough of those rows together and a hospital's true service area takes shape: not the boundary drawn on a map, but the actual distribution of where patients come from.

What Each Row Contains

Three measurements per hospital-ZIP pair.

Each record captures one hospital's Medicare inpatient activity from one ZIP code in one year. The three measurements in every row are the building blocks for every market analysis the dataset supports.

Total Cases
The number of Medicare inpatient discharges from patients residing in that ZIP code. This is the primary volume indicator — the count that defines how much of a hospital's patient base comes from each geography.
Total Charges
Gross charges billed for all inpatient stays from that ZIP. Not the amount paid — charges are the list price before any payer adjustments. Useful as a relative intensity measure when compared across ZIP codes for the same hospital.
Total Days of Care
The sum of inpatient days for all stays from that ZIP. Divided by total cases, it gives average length of stay for that ZIP's patient population — a proxy for clinical complexity that varies meaningfully across geographies.
The Questions It Answers

Market analysis starts with patient origin.

The dataset's value comes from what becomes visible when you look across hospitals rather than within a single one. Individual rows are facts. Combined, they reveal market structure.

01
How far does this hospital's reach extend?
The spread of ZIP codes with meaningful case counts shows whether a hospital draws patients from a compact local area or attracts them from a wide region. A tertiary medical center and a community hospital in the same city will look completely different on this map.
02
Which ZIPs send patients to multiple hospitals?
When two hospitals both show cases from the same ZIP code, that ZIP is a contested geography. Identifying the ZIPs where multiple hospitals compete for the same patient population is the foundation of any market share analysis.
03
How concentrated is a hospital's patient base?
Some hospitals draw most of their volume from a handful of nearby ZIPs. Others spread volume evenly across dozens. Concentration affects financial resilience — a hospital heavily dependent on a single ZIP is more exposed to demographic or competitive shifts there.
04
How has geographic reach changed over time?
With data available across multiple years, ZIP-level case counts can be trended. A hospital gaining cases from new ZIPs is expanding its service area. One losing volume from previously strong ZIPs may be facing competitive pressure or demographic decline in its core market.
Data Suppression

Low-volume rows are suppressed for patient privacy.

Not every hospital-ZIP pair has a visible case count. CMS suppresses rows where the volume is too low to publish without risking patient identification.

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What suppression means in practice
When a ZIP code contributes fewer than 11 Medicare inpatient cases to a hospital in a given year, CMS withholds the exact count. The row still exists in the data — the hospital-ZIP pair is recorded — but total_cases, total_charges, and total_days_of_care are marked as suppressed rather than populated with a number. This matters most for rural hospitals and low-density ZIP codes, where a meaningful share of rows may be suppressed. For large urban hospitals with high volume, suppression is minimal. Any market analysis should account for suppressed rows as a signal of low-volume geographies, not absent ones.
What Market and Geography Data Reveals

Three things geographic data makes visible.

Market Reach
How far does a hospital's draw extend?
The geographic footprint of patient origin — which ZIP codes contribute cases and at what volume — defines a hospital's true service area independent of any self-reported boundary.
Competition
Where are hospitals competing for the same patients?
ZIP codes that appear in multiple hospitals' service area records are contested geographies. That overlap is where market share is won and lost — and where shifts over time are most meaningful to track.
Trend
Is a hospital's geographic footprint growing or shrinking?
Year-over-year changes in which ZIPs send patients — and how many — show whether a hospital is expanding its reach, holding steady, or ceding ground in specific geographies.
About the Data

Annual snapshots going back to 2015.

CMS publishes the HSA file annually, covering Medicare inpatient activity from the prior calendar year. The dataset on this platform spans 2015 through 2024, enabling multi-year trend analysis at the hospital and ZIP level. Each year is a standalone snapshot — cases from one calendar year for patients discharged from that hospital during that period.

Coverage is limited to Medicare inpatient hospitalizations. Commercial insurance, Medicaid, and outpatient visits are not reflected. For hospitals serving a predominantly younger or commercially insured population, the HSA file will underrepresent total patient volume — but the geographic patterns it reveals remain a reliable proxy for overall market reach.

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