NASHVILLE, Tenn. -- A country singer who had popular hits in the 1990s has checked into a drug rehabilitation center.

In a statement on his Web site, John Michael Montgomery said he voluntarily checked himself into treatment for substance abuse due to severe anxiety attacks and sleep disorder.

Montgomery has canceled all concert dates and personal appearances for the next 30 days.

He said he's trying to defeat, "the demons that have stripped me of my energy of life and good health for so many years now."