Ramsay Health announced Mr Ramsay's illness in a statement to the ASX on Wednesday morning.

"On behalf of all Ramsay staff and doctors, we express our deep concern for Mr Ramsay," the company said.

"We will keep the market informed of Mr Ramsay's condition."

Mr Ramsay, who was valued by Forbes at $3.7 billion in March, is 78 years old.

He is the majority shareholder of Ramsay Health, which he founded in 1964 with a psychiatric hospital in Sydney.

Today the company has more than 150 hospitals located across five countries – Australia, England, France, Indonesia and Malaysia. It employs more than 30,000 people and admits over 1.4 million patients each year.

Mr Ramsay sold his 30 per cent stake in Prime Media in February, severing his long-standing ties with the media sector and netting around $96 million.

He owns 36.20 per cent of Ramsay Health, a stake worth $3.3 billion. The hospital group has been one of the best performers on the ASX, with its shares jumping more than four-fold in the last five years as it expanded to Europe and, more recently, Asia.

Mr Ramsay is single and does not have any children.

He founded Ramsay Health Care when he was just 28 years old. After completing his high school education at St Ignatius College Riverview, he initially attended Sydney University and studied law. But after working with his father, who was a property surveyor, on subdivisions, his focus quickly shifted.

Mr Ramsay's first major property purchase was a guest house on Sydney's North Shore, which he then converted into a 16-bed private psychiatric hospital, providing the foundation for Ramsay Health. He expanded the psychiatric hospital business before expanding into mainstream hospitals in 1978.

While the recent history of Ramsay has been a story of dramatic growth, the company's initial expansion was far less smooth.

The company went close to the fall not long after it floated in 1988, and Mr Ramsay took it private again in 1992 before it returned to the ASX five years later.

The ageing of Australia's population and a push by political parties of both persuasions to encourage consumers to take out private health insurance provided Ramsay with the momentum needed for growth, with legendary chief executive Pat Grier transforming the company from a minnow into a major player.

Mr Ramsay maintains a low media profile but as a longstanding supporter of the Liberal Party – he was the party's biggest donor in 2011-12, giving $605,000 in one year – he has never been far from the headlines.

Paul Ramsay founded Ramsay Health Care in 1964 with a single hospital in Sydney.