Assisted-suicide advocate Jack Kevorkian is back in prison after undergoing surgery for a double hernia, his attorney said Monday.

Mayer Morganroth said Kevorkian returned to the Thumb Correctional Facility in Lapeer on Sunday. Morganroth said Kevorkian will receive some follow-up treatment, but he didn’t know if it would be at the prison or elsewhere.

“They don’t really tell us. They just grab him and take him to the hospital,” Morganroth said.

Kevorkian, 76, is serving a 10- to 25-year sentence for second-degree murder after being convicted of giving a fatal injection to a Lou Gehrig’s disease patient in 1998.

He underwent surgery Friday at Foote Hospital in Jackson. Kevorkian was kept under guard and apart from other patients.

An outspoken advocate of doctor-assisted suicide for the terminally ill, Kevorkian has said he assisted in at least 130 deaths. The state revoked his medical license.

But he has promised in affidavits and requests for pardon or commutation that he will not assist in a suicide if he is released from prison. He is eligible for parole in 2007.

Gov. Jennifer Granholm has said she won’t consider pardoning Kevorkian.