Inequitable Conduct: 6 Costly Traps to Avoid

You spend years and a small fortune securing a patent, then win at trial on infringement – and still walk away with nothing, because a single withheld reference made the whole patent unenforceable. That is the sting of inequitable conduct, the defense patent litigators call the atomic bomb of patent law. It does not attack one claim; it can wipe out every claim in the patent, and sometimes related patents too. The good news is that the modern standard is demanding, and the conduct that triggers it is almost always avoidable with disciplined prosecution. Here is what every applicant, inventor, and in-house team needs to understand.

What Is Inequitable Conduct?

Inequitable conduct is an equitable defense that a defendant raises in patent litigation to argue that the patent owner obtained the patent through dishonesty before the U.S. Patent and Trademark Office. It is not a challenge to whether the invention is new or non-obvious. It is a challenge to how the applicant behaved during prosecution – whether they dealt with the examiner in good faith.

The defense flows from a basic bargain. Patent examiners rely heavily on what applicants tell them, so everyone substantively involved in a patent application owes the office a duty of candor and good faith under 37 CFR 1.56. Breach that duty in a material way, with intent to deceive, and a court can hold the entire patent unenforceable – even claims that have nothing to do with the misconduct.

That all-or-nothing consequence is why the defense carries such weight. Unlike an invalidity ruling that may knock out a few claims, a finding of inequitable conduct can render every claim unenforceable and, through what courts call infectious unenforceability, reach other patents in the same family.

The Therasense Standard: But-For Materiality and Intent

For years the defense was pleaded in nearly every patent case, because courts used a sliding scale – strong evidence of materiality could make up for weak evidence of intent, and vice versa. The Federal Circuit ended that in its landmark en banc decision, Therasense, Inc. v. Becton, Dickinson & Co. (2011), which tightened the standard dramatically.

Under Therasense, an accused infringer must prove two separate elements, each by clear and convincing evidence:

1. But-for materiality – the withheld or misrepresented information must be so significant that the examiner would not have allowed the claim had the truth been known. A reference that is merely cumulative of what the examiner already had does not qualify.
2. Specific intent to deceive – the patentee must have known of the information, known it was material, and made a deliberate decision to withhold or misrepresent it. Deceptive intent must be the single most reasonable inference from the evidence, not just one possibility among several.

Crucially, the two are no longer interchangeable. A mountain of materiality cannot substitute for proof of intent, and gross negligence is not enough. This is why post-Therasense findings of inequitable conduct are far rarer than they once were – the bar is high on purpose.

The Egregious-Misconduct Exception

Therasense left one important escape hatch. Where the applicant engages in affirmative egregious misconduct, the court does not require a separate but-for materiality showing – materiality is presumed. The classic example the court gave was filing an unmistakably false affidavit or declaration with the office.

The distinction matters. Simply failing to disclose a piece of prior art is judged under the strict but-for test. But fabricating test data, forging a declaration, or affirmatively lying about the state of the art is treated as egregious, and the deception is assumed to have mattered. Intent to deceive still must be proven, but the materiality gate falls away. The lesson is blunt: never let anything untrue go into the file.

Who Owes the Duty of Candor

One reason inequitable conduct catches people off guard is how many people carry the duty. It is not just the outside patent attorney. Under Rule 56, the obligation extends to each inventor named on the application, every attorney or agent who prepares or prosecutes it, and anyone else substantively involved – which can include in-house counsel, a research director, or a company executive who reviews the technology.

That breadth creates real exposure. An inventor who knows about a damaging prior sale, or an in-house lawyer who has seen a closely related reference from a parallel case, cannot stay silent and assume outside counsel will handle it. What each of those individuals knows is imputed to the application. Material information one person sits on can sink a patent that everyone else prosecuted flawlessly.

How Withheld Prior Art Triggers the Defense

In practice, the most common trigger is prior art the applicant knew about but did not disclose. The mechanism for disclosing it is the information disclosure statement, and a disciplined IDS practice is the frontline defense. If you know of a reference that a reasonable examiner would consider important, it belongs in front of the examiner – full stop.

This is where thorough searching quietly protects you. A rigorous prior-art search does more than test patentability; it builds a defensible record of what you found and disclosed. Litigation trouble usually starts with a reference that surfaces years later – one the inventor plainly knew about, that never made it into the file. The fix is not to hide references; it is to find them, evaluate them honestly, and disclose the material ones.

There is a strategic edge here for challengers too. An accused infringer running an invalidity search often uncovers exactly the kind of undisclosed, highly relevant art that supports both an invalidity attack and an inequitable conduct theory. The two frequently travel together.

Consequences and How to Protect Your Patent

When a court finds inequitable conduct, the results are severe. The patent becomes unenforceable in its entirety, the misconduct can spread to related patents in the same family, and in exceptional cases the court may declare the matter exceptional and award the other side its attorney fees. A defense that raises inequitable conduct can also drag prosecution counsel into the case as witnesses.

Avoiding all of this is mostly about process, not luck. Sound practices include:

• Disclose known material references promptly through a complete IDS – when in doubt, disclose.
• Search thoroughly and keep records of what was searched, found, and produced to the office.
• Verify every factual statement, affidavit, and declaration before it is filed; never overstate results.
• Brief inventors and in-house teams on the duty of candor so they flag relevant art instead of sitting on it.
• Cross-check related applications and litigation so art cited in one matter is disclosed in the others.

Handled this way, inequitable conduct becomes a defense you rarely have to worry about – because the honesty it demands is baked into how the patent was prosecuted in the first place. For challengers, the same discipline in reverse, paired with proceedings like inter partes review, turns a sloppy prosecution history into leverage.

How PerspireIP Can Help

Whether you are building a clean prosecution record or hunting the undisclosed reference that unravels an opponent’s patent, PerspireIP delivers the rigorous prior-art and invalidity searches that inequitable conduct disputes turn on. Talk to our patent team about protecting – or challenging – a patent.

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