Erik Menendez Recovering After Kidney Stone Surgery

Erik Menendez is on the mend after going under the knife for kidney stones ... TMZ has learned.

A rep for the California Department of Corrections and Rehabilitation tells TMZ ... Erik was transported to an outside medical facility on September 26. They tell us he's since been discharged and is back at Richard J. Donovan Correctional Facility in San Diego, where he remains in good condition.

A source confirmed to us Erik received treatment for kidney stones.

Erik's wife, Tammi, also hinted at the health scare earlier this week. She posted a video on Tuesday, and when someone asked in the comments how Erik was doing, she replied, "He just had another surgery but recovering. He is doing okay."

We broke the story ... Erik was hospitalized back in July for kidney stones, so this marks at least the second time in recent months he's needed medical treatment for the painful condition.

His attorney Mark Geragos had asked Governor Gavin Newsom at the time to have him released ahead of his parole hearing due to this serious medical condition. And as you know, both Erik and Lyle were eventually denied parole at their hearings.