The expansion includes a new 11-metre hydrotherapy pool and a 200-square-metre fully equipped rehabilitation gymnasium along with 10 specialist consulting suites.

Twenty modern private patient ensuite rooms have also been built, with the hospital now licensed for 57 beds.

Evolution Healthcare group marketing manager Gerry Murray said the additional wing was part of a three-stage redevelopment of the hospital since the organisation acquired the site in 2012.

"The first stage was the refurbishment of the existing hospital, which was in much need of an upgrade in order to meet the needs of the community," Mr Murray said.

"It's taken 18 months to complete this second stage of the hospital redevelopment and expansion.

"During the third stage of the master plan we will continue to expand services and facilities, including additional parking."

Mr Murray said Shellharbour Private was the sister hospital of South Coast Private in Wollongong.

"Evolution saw that between Nowra and Wollongong there wasn't any comprehensive surgical, medical and rehabilitation centre in one location to adequately service the needs of residents in Shellharbour and surrounding suburbs," he said.

"We thought, wouldn't it be wonderful to have a facility that offers all those services under one roof so patients can come here for their consultations, surgery and rehabilitation," Mr Murray said

"When we came to Shellharbour, the hospital was already overflowing with patients and through redeveloping the site we are able to better meet the needs of the community now, and into the future."

Shellharbour Private celebrates 40 years this month, after the facility was officially opened in April 1975.

Shellharbour mayor Marianne Saliba opened the new wing on Thursday evening at an event attended by Illawarra MPs, community leaders, healthcare providers and health fund representatives.

"Throughout the redevelopment we have had the support of consulting doctors, politicians and community members which has been great," Mr Murray said.