A lawsuit brought on behalf of mentally ill prison inmates states what should be the obvious: solitary confinement and mental illness make a combustible match.

After 13 inmate suicides and suicide attempts by isolated inmates in Massachussetts, including mentally ill inmate Mark Cunningham,lawyers have filed suit in federal court.

Mr. Cunningham’s case is one of 18 suicides and suicide attempts by inmates in solitary confinement described in a federal lawsuit filed Thursday by advocates for inmates and the mentally ill. They are seeking to prevent Massachusetts from placing mentally ill inmates in such segregated cells.

“We aren’t saying these folks should go free; we aren’t saying they shouldn’t be under high security conditions,” said Stanley J. Eichner, executive director of the Disability Law Center. But Mr. Eichner said putting prisoners in solitary conditions and denying them adequate mental health services was “literally the fatal flaw in the system.”

It's time to end the habit of putting mentally ill inmates in solitary confinement. It should be a no-brainer that confining a mentally ill person to 23 hours a day of isolation is going to be a death sentence, albeit one inflicted by his own hands.