To examine the prevalence of criminal thinking in mentally disordered offenders, incarcerated male (n = 265) and female (n = 149) offenders completed measures of psychiatric functioning and criminal thinking. Results indicated 92% of the participants were diagnosed with a serious mental illness, and mentally disordered offenders produced criminal thinking scores on the Psychological Inventory of Criminal Thinking Styles (PICTS) and Criminal Sentiments Scale-Modified (CSS-M) similar to that of non-mentally ill offenders. Collectively, results indicated the clinical presentation of mentally disordered offenders is similar to that of psychiatric patients and criminals. Implications are discussed with specific focus on the need for mental health professionals to treat co-occurring issues of mental illness and criminality in correctional mental health treatment programs.