The 75-year-old justice entered smiling, with a nod to the press box, and jumped in several times with questions at oral arguments for a total of two hours.
She looked bright and alert with her usual slightly raspy voice. At one point she amused the audience with a sarcastic question to veteran Supreme Court litigator Carter Phillips, which elicited laughter from the courtroom crowd.
Ginsburg has released two statements on her recent health scare, the latter one confirming the news that a small tumor had been removed from her pancreas revealing stage 1 cancer that had not spread to her lymph nodes.
In 1999, Ginsburg was treated for colon cancer but never missed a day of oral arguments despite aggressive treatments.
Later, she was quoted as saying, "There is nothing like a cancer bout to make one relish the joys of being alive."
Medical experts say Ginsburg was extraordinarily lucky that such a serious cancer was caught at such an early stage. The tumor was found during a routine screening as a follow-up to her earlier cancer.
Bunning's Startling Prediction
Ginsburg's return to work came a day after the Louisville Courier-Journal reported that U.S. Sen. Jim Bunning, R-Ky., predicted she would likely be dead from the cancer within nine months. Today, the senator apologized for the remarks and wished Ginsburg a speedy recovery.
But Ginsburg has yet to cancel two speaking engagements scheduled for mid-March, and cancer experts told ABCNews.com earlier this month that Ginsburg may have a better chance of surviving than most others with the illness.
The reason for the optimism is that the tumor found in the center of Ginsburg's pancreas was only about 1 centimeter in length, according to a statement from Memorial Sloan Kettering Hospital in New York City, where surgeons performed the operation to remove it.
A tumor of this size is about as small as is detectable by CT scan, said Dr. Paul Lin, a surgical oncologist specializing in pancreatic cancer at George Washington University Hospital in Washington, D.C.
"She is much more fortunate than most patients, who come in because of symptoms from their cancer," he said.
Ginsburg's High Chance of Survival
Dr. Joan Bull, a professor of oncology at the University of Texas Medical School in Houston, said the size of the tumor, which was discovered during a routine checkup in late January, suggests that the cancer was caught at a very early stage, possibly before it had had a chance to spread. If so, it would set Ginsburg, 75, apart from the 60 percent to 70 percent of pancreatic cancer patients whose disease is caught after it has spread to other areas of the body.
"If they did remove [the tumor] totally, with no lymph node or other vascular involvement, it does sound like a good outcome," Bull said, adding that treating pancreatic cancer at stage 1 gives patients a high chance of survival.
ABC News' Radha Chitale, Joanna Schaffhausen and Dan Childs contributed to this report.