In Dusky v. United States, the Supreme Court examined whether a defendant's mental illness could affect his ability to stand trial. Milton Dusky was convicted of assisting in the kidnapping and rape of an underage girl, but he appealed on grounds that he was not mentally competent during his trial. The court had previously found him "competent" based on a psychiatrist’s report stating that while Mr. Dusky suffered from schizophrenia, he understood the charges against him and was capable of assisting in his defense. The Supreme Court unanimously overturned this decision, ruling that it wasn't enough for a defendant to merely understand the charges; they must also have sufficient present ability to consult with their lawyer with a reasonable degree of rational understanding - including having a rational as well as factual understanding of proceedings against them. This case set new standards for determining when defendants are fit to stand trial by emphasizing both cognitive and functional aspects of competency.

The Dusky v. United States case did not have a dissenting opinion as the decision was unanimous. The Supreme Court ruled in favor of Dusky, stating that his mental illness at the time of trial made him unfit to stand trial and thus violated his Sixth Amendment rights to a fair trial.