This really isn ' t true at all . I work in a mental facility . We get people all the time coming through who don ' t actually have any mental disabilities . We know , after spending 12 hours a day with mental patients you get a feel for what is and isn ' t . If a person successfully pleads an insanity defense then what the judge decided is that they had a disease or disability that inhibited their reasoning . If a doctor feels that the disability in question is gone , then you no longer need to be in a facility designed to treat it , and are let out . Theoretically , you wont offend again , because the thing that made you offend in the first place is gone . Now , that being said , it is very hard to make an insanity plea stick unless the system you are working in is super corrupt . If you are admitted because of an insanity plea , you are probably truly unable to function in a larger society , and there is no hard or fast rule for how long that will take to cure , if it ever will be , or what . TLDR No , you wont spend your whole life in a psych facility due to an insanity plea . You will be released when you are cured .