The primary role of a forensic neuropsychologist in a competency evaluation is to determine whether the defendant has the capacity to understand the proceedings against them and to assist their attorney in their defense.

The three main criteria for determining competency to stand trial are: 1) the defendant's understanding of the nature and consequences of the charges against them, 2) the defendant's ability to assist their attorney in their defense, and 3) the defendant's rational understanding of the proceedings.

A variety of neuropsychological tests may be used to assess competency to stand trial, including the Wechsler Adult Intelligence Scale (WAIS), the Minnesota Multiphasic Personality Inventory (MMPI), the Rey-Kim Memory Profile, and the Wisconsin Card Sorting Test (WCST).

Forensic neuropsychologists face a number of challenges in conducting competency evaluations, including the lack of standardized criteria for determining competency, the difficulty in assessing competency in individuals with intellectual disabilities, and the influence of cultural factors on the assessment of competency.

Forensic neuropsychologists must take into account a number of ethical considerations when conducting competency evaluations, including the need to protect the defendant's rights, the need to ensure the accuracy of the evaluation, and the need to avoid bias and discrimination.