he first season of 90210, an American television series, began on September 2, 2008. Gabe Sachs and Jeff Judah are executive producers for the first season, after original producer Rob Thomas dropped out to focus on other projects. The series premiered to 4.65 million viewers, and broke records for The CW at the time, becoming their highest rated premiere in viewers and in Adults 18–49 with a 2.6 rating. On September 22, 2008, after airing just four episodes, the network gave the series a full-season order of 24 episodes.
Season one regular cast members include Rob Estes, Shenae Grimes, Tristan Wilds, Jessica Stroup, Dustin Milligan, Ryan Eggold, AnnaLynne McCord, Michael Steger, Lori Loughlin, and Jessica Walter. Along with special guests from the original series, Jennie Garth, Shannen Doherty, and Tori Spelling. Walter was replaced by Jessica Lowndes as a series regular in the thirteenth episode due to "financial reasons". The CW also hired Rebecca Sinclair to re-tool the series as head writer. She took over completely as executive producer by the end of the season, after Sachs and Judah resigned.
The season finale aired on May 19, 2009 and was seen by 2.00 million viewers. The season averaged 2.24 million viewers and a 0.9 rating in the Adults 18–49 demographic.Overview from themoviedb.org