The sixth season of the American television sitcom series It's Always Sunny in Philadelphia premiered on FX on September 16, 2010. It is the first season of the show to be filmed in high-definition. The season contains 14 episodes and concluded airing on December 16, 2010, with the hour-long Christmas special (which was produced for season 5, however aired as part of season 6). An additional episode called "The Gang Gets Successful" (production code IP06004) was produced for this season, but was not aired, despite scenes from the episode being included in promotional material for season 6. It was later re-edited with new scenes to create the season 7 episode "How Mac Got Fat".
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^ This episode is a direct to DVD, Blu-ray and digital download movie. It was released on November 17, 2009, and aired on December 16, 2010 on FX as the last episode of season 6. A video disclaimer on the Blu-ray release indicates it was not filmed in high definition, but was upconverted.</onlyinclude>
The sixth season received positive reviews. On Rotten Tomatoes, it has an approval rating of 94% with an average score of 8.3 out of 10 based on 16 reviews. The website's critical consensus reads, "Cleverly folding Kaitlin Olson's real-life pregnancy into the plot with characteristic perversity, It's Always Sunnys sixth season sees the Gang trying â and failing â to grow up."