In affirming the verdict, the Texas Court of Criminal Appeals rejected Penry's claims that the admission of language from the psychiatric evaluation violated his Fifth Amendment privilege against self-incrimination, and that the jury instructions were constitutionally inadequate because they did not permit the jury to consider his specific mitigating evidence.

[5] O'Connor expressed "considerable doubt" that the psychiatric report "even if erroneous, had a 'substantial and injurious effect'" on the outcome of the trial.

[6][7] However, the Court split 6-3 on whether the supplemental jury instructions on mitigating evidence were constitutionally adequate; the majority holding they were not.

[7] Thomas explained that he disagreed with the majority "...because I believe the most recent sentencing court gave the jurors an opportunity to consider the evidence Penry presented".

"[8] Subsequently to this case, the Supreme Court held in Atkins v. Virginia that execution of persons who are mentally retarded is unconstitutional.