JapanPre-existing condition reduction in accidents?
In Japan, compensation for personal injury from traffic accidents may be reduced if a pre-existing condition contributed to the harm, but only to the extent the condition actually worsened the outcome — not merely because it existed.
What the Law Says
Japanese law does not have a specific statute titled 'pre-existing condition reduction,' but courts apply general tort principles under the Civil Code to assess causation and damages when a victim has a prior health condition.
Under Article 722 of the Japanese Civil Code, a person who intentionally or negligently infringes another's rights must compensate for resulting damage. Compensation is based on actual harm caused by the tortfeasor’s conduct — not on the victim’s baseline health alone.
When a pre-existing condition (e.g., osteoporosis, prior spinal injury, or degenerative joint disease) interacts with an accident to produce greater harm than would occur in a healthy person, courts examine the degree to which the accident — not the pre-condition — caused the injury or disability.
A reduction in damages is only permissible where objective medical evidence shows the pre-existing condition materially contributed to the extent or duration of harm. Mere existence of a prior condition is insufficient grounds for reduction.
Statutory TextA person who has intentionally or negligently infringed the rights of others shall be liable to compensate for the damage thereby incurred.
— Civil Code, Art. 722 — Liability for Damages
What to Do
Obtain comprehensive medical records documenting both the pre-existing condition and post-accident injuries.
Request a causal relationship assessment from a qualified physician (e.g., orthopedic specialist or neurologist).
Ensure the medical report explicitly states whether and to what extent the accident aggravated the pre-existing condition.
Submit all evidence to the insurer or court before settlement negotiations or litigation begins.
Sources
Not legal advice. This article is general information based on publicly available sources, written for educational purposes. Laws change and individual situations vary. Consult a licensed attorney in your jurisdiction before acting on anything you read here. Last reviewed: 2026-06-09.