Uniondale-based Professional Physical Therapy said Friday it has purchased ProEx Physical Therapy, a group of 18 physical therapy and sports medicine offices based in Portsmouth, New Hampshire.

Terms of the deal were not disclosed.

With the purchase, Professional Physical Therapy has 135 centers in New York, New Jersey, Connecticut, New Hampshire and Massachusetts.

It has 25 Long Island locations.

The rapidly expanding outpatient physical therapy provider has made 25 acquisitions in the past six years.

The company has grown quickly through purchasing smaller therapy practices. Professional Physical Therapy was founded in 1998, and started to expand in 2011 when it went from 10 locations to 107 after it partnered with Greenwich, Connecticut-based private equity investor Great Point Partners.

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Great Point exited its deal with Professonal Physical Therapy late last year when another private equity firm, Boston-based Thomas H. Lee Partners, took a stake in the company.

Neither organization would comment on the size of that stake, although Adam Elberg, chief executive and president of Professional Physical Therapy said he is the single largest investor.

The ProEx acquisition will lead to further expansion in New England, Elberg said.

“We see these guys as a platform in Boston that we could build off of,” he said. “We are definitely going to continue expanding.”

ProEx clinics will continue to operate as ProEx Physical Therapy for now.

Mike Mulrenan, chief executive officer of ProEx Physical Therapy, will be a partner, and serve as the president of Professional’s Physical Therapy’s ProEx division.

Physical therapists are in high demand in Nassau and Suffolk counties, according to a state Labor Department forecast, which shows that the number of them is expected to climb 29 percent to 3,660 over a 10-year period that ends in 2022.