FAITH LAPIDUS: Professor Aday says older prisoners have to deal with aging in a difficult environment, especially one that does not necessarily meet their needs. And those needs can include treatment for mental health problems.

RONALD ADAY: "Many of the older inmates do have a lot of mental health issues -- alcohol, drug related, but also just depression and anxiety disorders. We have a lot of our veterans that have come back from different wars, Vietnam and others, that are older now. And they're, many of them, some of those might have been living in streets or they have post-traumatic stress issues. And a lot of those also end up incarcerated."

In the past, many of these people might have been sent to a mental hospital. But American society moved away from the idea of keeping people in such institutions. This was replaced with the idea of trying to treat them with medication in the community.

But as Professor Aday points out, today prisons seem in some cases to have taken the place of mental hospitals.

RONALD ADAY: "Because we have deinstitutionalized a lot of people from the mental health system, but in many cases the prison system has actually become responsible sometimes for taking care of some of those individuals."

CHRISTOPHER CRUISE: Taking care of older prisoners can be costly. But releasing them early might require changes in state and federal sentencing laws. California and other states are looking for ways to ease overcrowding and reduce their prison populations.