Competency to stand trial is an extremely complex issue, and practice has required that the psychiatrist play a major role in its determination. Several points should be emphasized:1. Because the law has provided only vague criteria, incompetency to stand trial has tended to be equated with mental illness by both psychiatrists and members of the legal profession.2. Many patients are presently hospitalized prior to trial although examination using the above criteria as guidelines would reveal them able to face their charges.3. The presence of mental illness does not preclude competency to stand trial. The defendant may show signs of mental illness and, indeed, even show delusional ideation, as long as it does not interfere with his comprehension of the courtroom proceedings and his ability to advise counsel.4. The issue of competency to stand trial is entirely separate from the problem of criminal responsibility and involves different legal tests.5. The psychiatrist does not make the decision as to the competency of an individual. His role is solely that of an advisor to the court. The criteria listed in this paper are offered as a guide for the examining psychiatrist. As with criminal responsibility, competency to stand trial is a subject for decision by the court on the basis of testimony it receives.Abstract Teaser