Kennedy, who was stricken with a brain tumor this summer, looked much thinner and a bit more frail, but he smiled and handled a few questions from reporters before walking into his Senate office to applause and a "Welcome Back Senator" sign hung by his staff.
"I feel fine," Kennedy said. "I'm looking forward to working with Barack Obama on health care. We're thankful for all the good thoughts and prayers we received."
Kennedy was flanked by his wife Vickie and his Portuguese water dogs, a regular presence around his Senate office.
Here's Kennedy's full statement, just released:
"It’s good to be back in the Senate. I am particularly looking forward to seeing my staff and my colleagues and to working in the current brief session on a realistic new stimulus package to help our fellow Americans who are suffering in this economic crisis.
"I will also continue to lay the ground work for early action by Congress on health reform when President Obama takes office in January. We’ve been making real progress in our discussions about a consensus approach, and I’m optimistic we’ll succeed.
"I am grateful for the prayers and good wishes I’ve received over the past several months. They have certainly lifted my spirits, as has the election of Barack Obama as our 44th President.”