Doctors announced that Kennedy had cancer on May 20 after he was hospitalized. The longtime chairman of the Health, Education, Labor and Pensions Committee underwent successful brain surgery at Duke University Medical Center on June 2 and has been undergoing cancer treatments in Massachusetts for the tumor.

Kennedy was greeted on the Senate floor by a long, sustained burst of applause from other senators and public visitors watching from the gallery.

“I return to the Senate today to keep a promise to our senior citizens – and that’s to protect Medicare.  Win, lose or draw, I wanted to be here,” Kennedy said. “I wasn’t going to take the chance that my vote could make the difference.”

His vote on the measure was seen as critical; the Senate fell one vote short of the needed 60 on June 26 when considering the bill that would have prevented a scheduled 10.6 percent cut to physicians who treat Medicare patients.

With Kennedy in the chamber this time to cast the decisive vote, several Republicans flipped and a procedural vote was approved, 69-30. The two party leaders had an agreement to then consider the legislation passed, based on the outcome of the vote.

Wearing a dark suit and a wide grin, Kennedy gave a grand gesture during the Medicare roll-call vote.

"Aye," he said, to laughter.

Kennedy looked fine and fit, shaking hands with a crowd of senators. His white hair was largely intact and perhaps even longer than before his absence.