The tragic events in Aurora, CO and Newtown, CT have renewed public perception of mentally persons as ‘dangerous’ and ‘criminal.’ Unfortunately, this perception is based more on conjecture and fear than research. The following essay takes stock of the empirical research on mental illness and criminal behavior. Three noteworthy trends emerge from this literature. First, the prevalence of mental illness is substantially higher among individuals who have come in contact with the criminal justice system relative to the general population. Second, individuals with psychotic and externalizing behavioral disorders, particularly those who also abuse drugs and alcohol, tend to engage in higher levels of violence than individuals with other forms of mental illness. Third, mental illness does not determine whether someone will break the law; rather, it is but one of many criminogenic risk factors that interact in complex ways to influence individual behavior.