The 83-year-old founder of Universal Health Services, America’s largest psychiatric hospital chain and a major acute-care hospital provider, too, is handing control of the King of Prussia-based company to his son.

Alan B. Miller will step down as chief executive in January and son Marc D. Miller, 50, will take his place in what the company said was as “long-planned succession.”

The senior Miller is generally credited with being a pioneer in purchasing hospitals in fast-growing communities and building a network out of them. Last year, the for-profit, publicly traded UHS had net income of $815 million on $11.4 billion in revenue.

“What changes? Not a whole lot,” said Marc Miller, who has served as president for 12 years. “We have a good rhythm here. We’re happy to continue with the same trajectory we’ve been on.”

The elder Miller founded what would become a Fortune 500 company in 1979 with a staff of six. Over four decades, UHS evolved into one of the nation’s largest health-care concerns. It now employs 90,000 and operates close to 400 facilities.

Fox Business identified Miller this year as the second longest-serving chief executive in the nation. He will continue to chair the UHS board of directors.

“I am certainly appreciative of the success we have achieved,” Alan Miller said. “I was an entrepreneur intent on doing meaningful work and making a difference with my life. It is an honor to hand over the reins of this very successful company and know that, every day, the team will continue to provide superior-quality care, save lives, and help families in their times of greatest need.”

Marc MiIler has been president of UHS since 2009 and headed the acute-care division, which includes 25 hospitals and accounts for half the firm’s revenue.

Marc Miler acknowledged that despite its international footprint, Universal Health Systems is little known outside the industry.

“We fly under the radar, and we take a conservative approach,” Marc Miller said. “For a company, we’re OK with that.”

Locally, UHS employs 850 people at its corporate headquarters and several thousand at hospitals in the Philadelphia region, which include the oldest psychiatric facility in the United States, Friends Hospital on Roosevelt Boulevard.

In addition to Friends, UHS operates eight additional psychiatric centers in the region: Brooke Glen Behavioral Hospital in Fort Washington; Fairmount Behavioral Health in Roxborough; Foundations Behavioral Health in Doylestown; Hampton Behavioral Health in Westampton, Burlington County; Horsham Clinic in Horsham; Keystone Center in Brookhaven; Lancaster Behavioral Health Hospital in Lancaster; and the Rockford Center in Newark, Del.

In July, UHS agreed to pay $127 million to the federal government to resolve a False Claims Act investigation of billing practices at about 30 of its psychiatric facilities. The deal followed a report in the BuzzFeed News that the chain would exaggerate the mental plight of patients to hold them involuntarily until their insurance money ran out.

Marc Miller said UHS has no designs on acquiring an acute-care hospital in the Philadelphia region.

“We’re pretty opportunistic about what markets we go into for each of our business lines,” he said, adding that UHS had looked at buying Hahnemann Hospital in Center City but passed on it. “We’ve not seen the opportunity in this market to enter the acute-care space, though we’d love to have more of a footprint here.”

During his tenure in charge of operations at UHS, Marc Miller has focused on hiring senior executives who have worked “out in the field” at the company’s hospitals.

“That way, our executives are much more empathetic to the folks servicing patients every day,” he said. “It has made us a better company.”

Compay shares have traded in a range of $65.20 to $157.06 in the last year, and closed Tuesday down 3.74%, to $109.32, on the New York Stock Exchange.