Wall Street financier Bernie Madoff has been moved to the medical centre within the prison where he is serving 150 years for fraud, BBC reported.
He was transferred on 18 December, a spokeswoman for the Butner Federal Correctional Complex in the US state of North Carolina confirmed.
However, she declined to provide further details.
Madoff, 71, is serving the prison term after pleading guilty to a $65bn (£41bn) fraud.
He admitted defrauding thousands of investors through a Ponzi scheme, which pays out using investors' money, rather than from any actual profits.
He said the scheme had been running since the early 1990s.
It unravelled when Madoff's investors, hit by the economic downturn, tried to withdraw about $7bn, but he could not produce the money.
The list of his victims included film director Steven Spielberg's charitable foundation.