Mad Men drew record audience ratings for AMC with the first episode of the fifth series on March 25.
The advertising drama brought in 3.5 million viewers for the cable network, making it the most watched episode in the show's history.
The show returned after at 17-month break with a double episode which scored a 1.6 rating in the 18-49 demographic, an improvement on its fourth season premiere episode.
The fourth season of Mad Men averaged 2.3 million viewers and a 0.9 rating.
AMC president Charlie Collier said: "Mad Men set the bar high and we are incredibly proud that it continues to engage audiences looking for unexpected, unconventional and uncompromising television."
A further 900,000 watched the repeat of the season five opener at 11pm, bringing the total viewership to 4.4 million.