Eleven percent of American children have trouble breathing at night, and it could be because of their tonsils, according to a new study.

“The hallmark is snoring,” said Dr. Max April, with the Weill Cornell Medical Center.

Snoring is the key sign the tonsils and adenoids are to blame, according to the study. They clog breathing passages, and doctors warn that Attention Deficit Hyperactivity Disorder can be a by-product of sleep apnea, but it's not a symptom.

A mother, identified only as Kim, said her two boys had difficulty breathing at night. Snoring would wake them up, making them tired during the day.

Like his brother, Andrew, 7-year-old Will had enlarged tonsils that blocked his air-flow. Doctors removed his tonsils, which improved his sleep immediately, Kim said.

The study found that removing tonsils and adenoid glands helped long term.

“The majority of improvement continued even two and a half years after surgery. And I suspect when they do the next study at five years, it will continue,” April said.

Pediatric sleep apnea is a relatively new problem, according to WRAL Health Team Physician Dr. Allen Mask.

“Prior to the 80s, many kids had their tonsils removed because of infections. Today, better medicines mean more kids have their tonsils,” he said.

Tonsillectomies aren't performed as much as they used to be. However, it remains the most common major operation performed on children in the United States, ranking just above getting ear tubes.