What rare disease coding costs.
Most rare diseases have no ICD-10 code of their own. They are filed under a broader code, alongside dozens of other diseases. ICD-10 Map shows which code a rare disease lands on, how many others share it, and whether a more specific ICD-10-CM code already exists.
What happens when a rare disease is coded
Measured across 8,980 rare diseases on ICD-10-CM, the code set US claims use.
Two different problems
- Fixable: 4,121 diseases (41.1%). The mapped code is not billable, but a more specific child code exists. ICD-10 Map shows it.
- Irreducible: the 72.8%. The code is valid and there is nothing better. Once coded, the disease cannot be told apart from the others under the same code, so keep the ORPHAcode alongside it.
Find a disease by the name you know
Formal names are not always the ones clinicians use: CADASIL is stored formally as “cerebral arteriopathy, autosomal dominant, with subcortical infarcts and leukoencephalopathy”. ICD-10 Map searches 22,643 names and synonyms for the 8,980 diseases, so the clinical name finds it.
Sources
Built from Orphanet, MONDO and ICD-10-CM FY2026 from CMS. No account needed.
ICD-10 Map is a reference, not a coding authority. Check codes against the official ICD-10-CM tabular list before submitting a claim.
Common questions
Do rare diseases have their own ICD-10 codes?
Most do not. In ICD-10-CM most rare diseases are filed under a broader code shared with other diseases. For example, Q87.0 carries 154 distinct rare diseases.
What is the difference between ICD-10 and ICD-10-CM?
ICD-10 is the World Health Organization's classification. ICD-10-CM is the US clinical modification used on US medical claims. ICD-10 Map uses ICD-10-CM FY2026.
What is an ORPHAcode?
An ORPHAcode is Orphanet's identifier for a rare disease. Because an ICD-10 code often cannot tell rare diseases apart, recording the ORPHAcode alongside it keeps the diagnosis precise.
What does billable mean?
A billable ICD-10-CM code is specific enough to be used on a claim. Codes with more specific child codes beneath them are not billable.
Is ICD-10 Map free?
Yes. It is free, runs in your browser and needs no account.
Before the code comes the diagnosis.
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