Glossary
Eggshell plaintiff rule
The rule that a person who causes an injury is responsible for all the harm it does, even if the injured person was unusually fragile, for example because of an old injury or an illness.
General information, not legal advice. Talk to a licensed attorney in your state.
Quick answer
The eggshell plaintiff rule, also called the thin skull rule, says that a person who causes an injury is responsible for all the harm it does, even if the injured person was unusually fragile. The person at fault must, in the words of Cornell's Legal Information Institute, "take the victim as they find them."
In a car accident claim#
The rule comes up when the injured person had a Pre-existing condition. A health problem you had before the crash. You generally cannot claim for the condition itself, but you can claim for the extent to which the crash made it worse. Glossary, such as worn spinal discs, an old neck injury, brittle bones or an illness. The insurer cannot argue that a healthier person would have walked away. California's civil jury instructions, for example, tell jurors to decide the full amount of damages even if the injured person was more susceptible to injury than a normally healthy person would have been.
The rule has limits. The at-fault driver does not pay for the old condition itself, only for the harm the crash caused, including making the condition worse. California's instructions allow damages for the effect of the crash on a physical or emotional condition that it made worse. So the dispute usually turns to Causation. The link between someone's careless act and your injury. You must show the crash caused the harm you are claiming. Glossary: how much of the current problem is new. Our injuries hub and the guide to back and neck injuries explain how medical records show that difference.
Example#
Related terms#
Questions people ask
Does the eggshell plaintiff rule mean the other driver pays for my old injury?
No. It covers the harm the crash caused, including making an old condition worse, but not the condition you already had. Medical records from before and after the crash usually show the difference.
Is the thin skull rule the same as the eggshell plaintiff rule?
Yes. They are two names for the same rule. Courts and lawyers also call it the eggshell skull rule.
Sources
- Cornell Legal Information Institute, Wex: eggshell skull rule — definition of the rule
- Judicial Council of California, Civil Jury Instructions (CACI) 2026 — No. 3927 (aggravation of a preexisting condition) and No. 3928 (unusually susceptible plaintiff)
Last reviewed October 29, 2026 by the Accident Claim Facts editorial team. Found an error? Tell us.
Keep reading
- GlossaryGlossaryShort, plain-English definitions of the legal and insurance terms that come up after a crash, each with an example, related terms and the sources behind it.
- Injury typesInjury typesHow common crash injuries are documented and proven, why some symptoms appear later, what maximum medical improvement means and how the type of injury shapes…
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- GlossaryExemplary damagesTexas's term for punitive damages, awarded only for fraud, malice or gross negligence, and capped by statute.
- GlossaryFinancial responsibilityA state rule that drivers must be able to pay for crash damage they cause, usually shown with an insurance policy or other approved proof.