He quit smoking a long time before, but fell into a short-term habit during 9/11. Feeling weak and exhausted due to the emotional trauma during that day. Peter mentioned this in his final World News Tonight broadcast.
Anyone watch the Emmy awards last week when they did a final tribute to Peter? It was also a tribute to the old guard of the "Big 3" network news anchors (Jennings, Rather, and Brokaw) but everyone knew they did most of the focus on Peter, as the 2 survivors came on stage to talk about the past, present and future of broadcast news on TV. Things have sure changed with the advent of cable, and internet I say. But they seemed to respect the changes though.