The short answer: it depends on the court
People often assume polygraph results are either always banned in court or always allowed. Neither is true in the United States. There is no single national rule. Many courts exclude polygraph evidence or restrict it heavily, mainly because of doubts about its reliability, but rules differ between federal courts, state courts and military courts.
This guide explains the one Supreme Court decision that matters most, shows how one state handles it very differently, and explains what to do if a legal matter involves a polygraph. It is general information, not legal advice.
United States v. Scheffer (1998)
The key case is United States v. Scheffer, decided by the Supreme Court on March 31, 1998. An Air Force airman had been convicted at a court-martial. The military judge excluded his polygraph evidence under Military Rule of Evidence 707, which bars polygraph results, an examiner's opinion and any reference to taking or offering a polygraph in court-martial proceedings.
| What the Court decided | |
|---|---|
| The question | Does a blanket ban on polygraph evidence in military trials violate an accused's constitutional right to present a defense? |
| The answer | No. The Court held Rule 707 constitutional. |
| The reasoning | The ban serves the legitimate aim of excluding unreliable evidence. The Court said the scientific community remains "extremely polarized" about polygraph reliability. |
| The limit | The decision concerned a military rule. It does not create a nationwide ban in civilian courts. |
The Court's reasoning was shared by a majority in parts and by a plurality in others, and Justice Stevens dissented, so the opinion is worth reading in full if your case turns on it.
Why many courts are cautious
- Reliability is disputed. The National Research Council found accuracy "well above chance, though well below perfection," and that screening accuracy is almost certainly lower. See how accurate a polygraph really is.
- No way to check a single result. Scheffer noted there is no reliable way to know whether a particular polygraph conclusion is accurate.
- Weight, not just admissibility. Even when allowed, a judge or jury may give the result little weight.
An example of a different approach: New Mexico
New Mexico has a detailed evidence rule, Rule 11-707, that allows a qualified examiner to give an opinion on truthfulness, but only if strict conditions are met. According to a reference copy of the rule:
- The examiner is qualified, with experience or equivalent training and a current polygraph license.
- Results are scored quantitatively, using a method polygraph experts generally accept as reliable.
- At least two relevant questions were asked and at least three charts were recorded.
- The whole session, including pre-test and any post-test interview, was recorded.
- A party planning to use the evidence gives written notice at least 30 days before trial, with the report, charts and recording.
- The court decides admissibility outside the jury's presence, and no witness can be forced to take a polygraph.
This shows that "admissible" can still mean a heavily conditioned, carefully scrutinised process. It is an example from one state, not a rule for the country. Check the official text and the rules where your case is.
What this means if a legal matter involves a polygraph
- Do not assume either way.Whether a result can be used depends on the court, the type of case and the rules that apply.
- Speak to a lawyer in your jurisdiction first.Before taking a private test, offering one or agreeing to one, get advice on how it could be used and what happens if the result is bad.
- Remember that statements count.What you say in a pre-test or post-test interview may be treated differently from the chart. Be accurate and consistent.
- Keep every document.Reports, charts, questions and any recording, since the quality of the test can matter as much as the result.
- Do not rely on a result you cannot explain.If a polygraph is part of your case, understand how it was run and what it does and does not show.
Related reading
For workplace rules, see polygraphs in the workplace: your legal rights, and for the science behind the debate, why polygraphs fail innocent people. If you are working with counsel, see how a lawyer can use independent polygraph scoring.
This guide is general information about US law, not legal advice. Rules vary by court and change over time. The New Mexico summary relies on a reference copy of the rule; check the official text.
Frequently asked questions
Are polygraph results admissible in US courts?
What did the Supreme Court decide in United States v. Scheffer?
Does Scheffer ban polygraphs in all US courts?
Is there a US state that allows polygraph evidence?
Can I use a private polygraph in my defense?
Sources
Need to understand a polygraph in a legal matter?
A lawyer advises on admissibility and strategy. In a private 1-on-1 session we can explain how the test works and what a result does and does not show, so you can have a better conversation with your lawyer.