In the typical criminal case where a police officer makes a warrantless arrest during or shortly after a criminal episode, two factors apply to a person suspected of being mentally retarded. The first factor relates to whether the officer had probable cause to arrest and the second factor is whether an arrest actually occurred. If the police had probable cause to arrest and an arrest occurred, then police are required to read the Miranda warnings to a suspect. With a retarded person, for whom suggestibility and compliance with authority figures is common, it is likely that any detention by the police constitutes an arrest, so Miranda warnings are important when the police start asking any questions after the detention of a person who might be mentally retarded. The handling of incompetency to stand trial is particularly difficult with mentally retarded persons, because their condition is basically unchangeable. If trial competence cannot be achieved within 6 months of treatment, the state should be required to dismiss the charges or proceed to a trial governed by procedures that will compensate for the defendant's incompetence. In the case of plea negotiations involving mentally retarded persons, special effort must be taken to ensure that the accused does comprehend the nature of any constitutional rights waived by pleading guilty. To establish the defense of insanity in showing that a mentally retarded person lacked criminal responsibility in an incident, a causal connection must be established between the condition of mental retardation and the defendant's inability to control his/her behavior. Mental retardation may also be argued as a mitigating circumstance to reduce sentence severity. A list of general suggestions for handling mentally retarded persons in the criminal justice system is also provided, along with 17 notes.