Neuroimaging and other neurobiological evidences are increasingly introduced in criminal litigation, especially when a neuropsychiatric disorder is suspected. Evaluations of criminal competencies are the most common type of criminal forensic assessment in forensic psychiatry and psychology. Given this, it is critical for forensic evaluators to understand how neuropsychiatric disorders may affect a defendant's criminal competencies and how neurobiological data may be used in competency determinations. This paper reviews the use of neurobiological data, particularly neuroimaging, while considering the limitations and potential misuse of such data in criminal competency evaluations.