Nix v. Whiteside, 475 U.S. 157 (1986), was a United States Supreme Court decision that dealt with the effective assistance of counsel during a criminal trial.

Whiteside was convicted, and subsequently applied for a federal writ of habeas corpus, on the grounds that his conviction was tainted under the Sixth Amendment in that his attorney's threat to disclose the perjury had deprived Whiteside of effective assistance of counsel.

The majority opinion, written by Chief Justice Burger, stated that an attorney's duty to his client's cause is "limited to legitimate, lawful conduct compatible with the very nature of a trial as a search for truth", and that "the right to counsel includes no right to have a lawyer who will cooperate with planned perjury".

Concurrences by Justices Blackmun, Brennan and Stevens stated that Whiteside had failed to show that the attorney's actions had caused prejudice to the defendant's trial required to sustain a claim of "ineffective representation", as required by the case of Strickland v. Washington, 466 U.S. 668 (1984).

"Unfortunately, the Court seems unable to resist the temptation of sharing with the legal community its vision of ethical conduct."