Dallas police are investigating the aggravated sexual assault of a 13-year-old girl at Timberlawn, the psychiatric hospital in East Dallas that has a long record of safety problems.

Officers were called to the hospital on Samuell Boulevard on Monday evening, a police spokeswoman said, adding that she could not release details because of the nature of the offense. No one had been arrested in the case.

Timberlawn’s chief executive, James Miller, would not speak to a reporter. He issued a statement saying, “The care and safety of our patients, including their privacy, is Timberlawn Behavioral Health System’s top priority.” Miller said the hospital was cooperating with investigators.

The Texas agency that oversees hospitals will look into the matter, said Carrie Williams, spokeswoman for the Texas Health and Human Services Commission. In 2015 the agency threatened to shutter Timberlawn for safety violations, and it currently has the hospital on probation, she said.

Universal Health Services Inc., a corporation that trades on the New York Stock Exchange and is valued at $10 billion, owns Timberlawn. A spokeswoman for the company, the country’s largest for-profit provider of mental health services, did not respond to a request for comment.

Timberlawn treats patients as young as 12 for serious conditions including depression, trauma and anxiety, according to its website. The sprawling 100-year-old hospital, shaded by tall trees and anchored by a stately white farmhouse, has 144 beds. Timberlawn did not respond to questions about how many patients it was currently treating.

In the last three years, a string of patients and staff members have been put at risk at Timberlawn. Two have died.

Last year, a patient tackled a doctor and slammed her head against the floor. She died two days later. In 2015, hospital inspectors found that two patients had had a sexual encounter and others had been violent. During one inspection, the staff couldn't account for the whereabouts of six patients.

In 2014, a woman who had told staff members that she was suicidal was left unobserved. She hanged herself with a sheet and died.

A Dallas Morning News analysis of hospital inspection data last year found that safety problems have plagued more than a quarter of Universal Health's 154 hospitals that received federal funds to treat the poor and elderly. Thirteen of those hospitals are in Texas.

Health officials shut off Timberlawn’s federal funding in 2015. Texas ordered Timberlawn to surrender its license and fined it $1 million.

But as is customary, the hospital was allowed to appeal.

Timberlawn’s federal funding was restored. The state health agency cut its penalty to $193,000 plus probation a year ago, its spokeswoman said, because of the work the facility had done to improve patient safety.

If health inspectors find deficiencies during the three-year probation period, the state could again suggest revoking the hospital’s license, which runs through August 2019.