His family said in a statement released to The Associated Press that the 85-year-old Paterno continues to undergo a "regimen of treatments" after being diagnosed two months ago with what they call a treatable form of lung cancer.
The family hoped his latest stay would be brief. He most recently was in the hospital last month after breaking his pelvis.
The family said Paterno had "total confidence" in his doctors and was determined to make a full recovery.
School trustees fired Paterno on Nov. 9 in the aftermath of child sex abuse charges against retired defensive coordinator Jerry Sandusky.
In related news, the Washington Post announced Friday that it will be releasing an exclusive interview with Paterno Saturday at 4 p.m. It is being billed as Paterno's "first extensive interview" since the Sandusky scandal broke.