Super Bowl XLV was the most watched TV programme in American history

"The world's greatest sporting event has cemented its place in pop-culture history by netting the most amount of Americans to ever watch a TV show. And not even Christina Aguilera's flub or Groupon's offensive ad could do anything about it.
In fact, they probably contributed to the 111 million viewers that tuned in for Sunday's thrilling Super Bowl between the victorious Green Bay Packers and Pittsburgh Steelers. The NFL's showpiece game actually broke its own record, with five million more tuning in this year compared to 2010's showdown between the New Orleans Saints and Indianapolis Colts.
Until then, the series finale of M*A*S*H had famously held the record for 27 years with an impressive tally of just under 106 million, but now the Super Bowl has taken over the top two spots, as well as numbers four and five. "Super Bowl XLV caps what is arguably the most successful season that any sports league has ever had," said Pat McDonough, senior vice president for insight and analysis at the Nielsen Co. "The number of people watching NFL games has never been higher, with 24% more people watching the average NFL game this year than just five years ago. The Super Bowl continues to be in a category of its own.""
Source:  Time, 8th February 2011
Earlier - Super Bowl XLIV was the most watched TV programme in American history