California Civil Jury Instruction CACI 3928, titled “Unusually Susceptible Plaintiff,” tells jurors that a defendant must fully compensate a plaintiff for all harm caused by wrongful conduct, even when the plaintiff was more vulnerable to injury than a normally healthy person would have been. It is the California codification of the “eggshell plaintiff” or “thin skull” rule: you take your victim as you find them. A note on a common mix-up before going further — several online sources describe CACI 3928 as the instruction covering loss of consortium for unmarried partners. That is wrong. CACI 3928 has nothing to do with relationship status.
What the Instruction Tells the Jury
The instruction directs the jury to “decide the full amount of money that will reasonably and fairly compensate [the plaintiff] for all damages caused by the wrongful conduct of [the defendant], even if [the plaintiff] was more susceptible to injury than a normally healthy person would have been, and even if a normally healthy person would not have suffered similar injury.”1Justia. CACI No. 3928. Unusually Susceptible Plaintiff
One sentence, but it does heavy work. It removes the defense argument that a plaintiff’s injuries are somehow their own problem because of an underlying condition. If a negligent driver rear-ends someone with fragile bones, the driver pays for the fractures, not for the bruise a healthier person would have walked away with.
The instruction does not eliminate causation. The plaintiff still has to prove that the defendant’s wrongful conduct caused the harm. But once that link is established, the full scope of the injury is compensable, no matter how much the plaintiff’s pre-existing susceptibility amplified it.
When the Judge Reads It
CACI 3928 is not part of every personal injury trial. A judge includes it only when the evidence puts the plaintiff’s unusual susceptibility into play. Typical situations:
- A pre-existing spinal or joint condition, where a collision that would produce temporary soreness in most people triggers a severe disc herniation in someone with degenerative disc disease.
- A psychological vulnerability, where a traumatic event causes debilitating PTSD in a plaintiff with a documented history of anxiety or prior trauma while the same event might cause only temporary distress in someone else.
- An immune or metabolic disorder that turns a relatively minor physical injury into a prolonged recovery or secondary complications.
- Age-related fragility, where an elderly plaintiff fractures bones and needs surgery from an impact that would merely bruise a younger person.
In each of these, the defense will typically bring medical evidence suggesting the plaintiff’s condition, not the defendant’s conduct, is the real reason the outcome was so severe. CACI 3928 tells the jury that vulnerability is not a valid basis for reducing the award.
What the Defense Can Still Argue
The eggshell rule is powerful, not unlimited. Even with CACI 3928 in the instructions, defendants retain several legitimate arguments.
They can argue that certain symptoms existed before the incident and were not worsened by it. CACI 3928 covers aggravation of a pre-existing condition. It does not require compensation for symptoms already present and unchanged. If chronic back pain was at the same level before and after the accident, the defense can argue there is no additional injury to pay for.
They can also challenge causation itself. The instruction assumes the jury has already found the defendant liable for causing the harm. If the defense can show that the worsened condition came from an unrelated cause, such as a separate fall or the natural progression of a disease that would have happened anyway, CACI 3928 does not override that evidence.
Comparative fault still applies. If the plaintiff bears some share of responsibility for the incident, the jury reduces damages by that percentage. The eggshell instruction does not shield the plaintiff from California’s comparative negligence framework.
How It Interacts With Other Damages Instructions
CACI 3928 sits within the 3900 series of California Civil Jury Instructions, which covers damages generally. It works alongside instructions that spell out specific damage categories. CACI 3920, for example, governs loss of consortium for spouses, addressing losses like love, companionship, comfort, care, affection, and moral support.2Justia. CACI No. 3920. Loss of Consortium (Noneconomic Damage) The 3903 series addresses economic damages, including lost earnings and household services the plaintiff can no longer perform.3Justia. CACI No. 3903E. Loss of Ability to Provide Household Services (Economic Damage)
When CACI 3928 applies, it amplifies all of those. The jury is told to award the full amount in every applicable category, even if a normally healthy person would not have suffered those losses at all. A susceptible plaintiff may accumulate far higher medical bills, miss far more work, and lose far more consortium than an average person. CACI 3928 tells the jury that every dollar of that enhanced harm counts.
The Mislabeling Circulating Online
A number of online sources identify CACI 3928 as the jury instruction for loss of consortium claims by unmarried cohabitants. That is not what CACI 3928 does. The loss of consortium instruction for spouses is CACI 3920, and no separate numbered CACI instruction exists specifically for unmarried cohabitants.2Justia. CACI No. 3920. Loss of Consortium (Noneconomic Damage)
The confusion probably grew out of a real question: whether unmarried partners can sue for loss of consortium in California. They can, but the authority comes from case law, not a CACI number. The 1983 appellate decision in Butcher v. Superior Court held that “an unmarried cohabitant may state a cause of action for loss of consortium by showing that the nonmarital relationship is both stable and significant.”4Justia Law. Butcher v Superior Court (Forte) Courts look at how long the couple lived together, whether they shared finances, and whether they held themselves out as committed partners.
Registered domestic partners are treated differently. Under California Family Code Section 297.5, registered domestic partners have the same rights as spouses, so they use CACI 3920 directly rather than the Butcher framework.5California Legislative Information. California Family Code 297.5 Unmarried partners who have not registered a domestic partnership must meet the “stable and significant” standard from case law.
One boundary worth flagging: unmarried, unregistered partners generally lack standing to file wrongful death claims in California. The wrongful death statute limits standing primarily to spouses, registered domestic partners, and children. A cohabitant’s consortium claim applies when the partner is injured but alive, not when the partner has died.