Williams discussed knee replacement surgery in a story by Dr. Nancy Snyderman on NBC's "Nightly News" on Thursday, saying, "If you don't see me around here for a while, this is the reason why."
The anchor of television's top-rated evening news show said he's had three previous surgeries on his right knee, but the pain was becoming more of an issue. When it began costing him sleep, Williams said he realized it was time to take care of it. Williams is 54.
Lester Holt will fill in for him. NBC isn't saying when the surgery will be.