Cygnet Healthcare, part of Universal Health Services (UHS), has acquired Alpha Hospitals for £95m.
The acquired business, which provides specialist psychiatric care in England, adds four hospitals and 305 beds to the Cygnet family.
Universal Health Services board chairman Alan Miller said: "We are pleased to announce the acquisition of Alpha and welcome them into our growing system in the UK.
"The facility locations are an excellent geographical fit and their services are complementary to Cygnet’s existing portfolio."
Alpha has modern facilities in Bury and Sheffield, which offers child and adolescent services, low and medium secure services, as well as various specialist mental healthcare services.
With the current deal, UHS hospitals will have a total of 21 facilities and 1,100 beds in the UK.
Cygnet Healthcare CEO David Cole said: "Alpha Hospitals has a very good pedigree and an excellent reputation in the sector. Like Cygnet, it is a brand that portrays quality and confidence, and boasts very strong customer relationships."
In 2014, UHS acquired Cygnet Healthcare, which is claimed to be one of the largest independent providers of behavioural health services in the UK.
Through its subsidiaries, UHS operates behavioural health facilities, acute care hospitals and ambulatory centres in the US, Puerto Rico, the UK and US Virgin Islands.