A doctrine that extends the exclusionary rule to make evidence inadmissible in court if it was derived from evidence that was illegally obtained. As the metaphor suggests, if the evidential "tree" is tainted, so is its "fruit." The doctrine was established in 1920 by the decision in Silverthorne Lumber Co. v. United States, and the phrase "fruit of the poisonous tree" was coined by Justice Frankfurter in his 1939 opinion in Nardone v. United States.

Like the exclusionary rule itself, this doctrine is subject to three important exceptions. The evidence will not be excluded:

1. if it was discovered from a source independent of the illegal activity;
2. its discovery was inevitable;
3. or if there is attenuation between the illegal activity and the discovery of the evidence.

Further, if the primary evidence was illegally obtained, but admissible under the good faith exception, its derivatives (or "fruit") may also be admissible.