Correctional staff play an important role in the assessment of inmates and probationers by serving as sources of information for mental health professionals. Correctional staff are in a unique position to observe inmate behavior since they interact with and see inmates in various situations and contexts. Mental health diagnosis and assessment of offenders is facilitated by the DSM-IV, a multiaxial system in which people are diagnosed along several different dimensions or axes. The DSM-IV can be used to evaluate mood disorders, psychotic disorders, mental retardation, personality disorders, substance abuse and dependence, and suicide. Once an offender is referred to a mental health professional, several techniques can be used to evaluate the problem, including interviews, intelligence testing, and personality tests. Legal issues associated with mental health assessment are examined, with emphasis on not guilty by reason of insanity cases and competency to stand trial.