The difference between an insanity acquittal and a GBMI verdict is that under an insanity acquittal, the defendant is incapable of the mental state required to commit an act punishable by law. The GBMI verdict, on the other hand, finds the defendant guilty of an offense and mentally ill, but not insane at the time the crime was committed. Under the GBMI verdict, the court may impose any sentence appropriate for the offense. During the serving of the sentence, the GBMI offender will receive psychiatric treatment. The sentence must be completed, however, even though the offender may be discharged from psychiatric treatment. Constitutional attacks on GBMI statutes have been based in violations of equal protection, due process, and prohibition against cruel and unusual punishment. Functional problems with the GBMI verdict pertain to burden of proof, procedures, jury confusion about the difference between mental illness and legal insanity, and the extent to which GBMI requires psychiatric treatment. Of the nine GBMI defendants currently incarcerated in South Dakota, eight have received or are now receiving mental health treatment. Jury instructions should distinguish between legal insanity and mental illness, and psychiatric treatment for GBMI defendants should be provided by prison authorities. Another constitutional challenge to GBMI may pertain to the due process right to a civil hearing prior to commitment to a mental health facility. 120 footnotes.