The previous high was established with season 4's premiere, for which just over 2.9 million tuned in. Viewership from the most recent episode, last season's finale (way back in October 2010!), increased by more than a million.
AMC is obviously thrilled, and issued an enthusiastic statement on Monday via network head Charlie Collier: "Mad Men set the bar high, and we are incredibly proud that it continues to engage audiences looking for unexpected, unconventional and uncompromising television. For each of the five Mad Men seasons, Matthew Weiner and his team have crafted a beautifully told story, and each season a larger audience has responded; a rare accomplishment. We couldn’t be more proud of this program, the brilliant writers, cast and crew, and the entire team on each side of the camera."
What's interesting, though, and no doubt weighing on the minds of AMC's higher-ups, is the fact that while the season 5 premiere of Mad Men was a huge success numbers-wise, the network's other beloved series, The Walking Dead, routinely pummels Mad Men's ratings. For example, the two series' most-watched episodes are separated by roughly 5.5 million viewers. Needless to say, AMC hopes that Sunday night's ratings spike for Mad Men is just the beginning.