Girls has been described as a "brilliant gem" and "like nothing else on TV" by US TV critics since it launched last month.
The show follows the "humiliations and rare triumphs" of four girls Hannah, Marnie, Jessa and Shoshanna, who all love in New York.
Hannah, played by Lena Dunham, is described as a "mixture of self-entitlement and self-loathing" and is a wannabe writer. Allison Williams plays Marnie, Hannah's roommate and best friend, who has a job and a serious boyfriend.
Jemima Kirke is cast as Jess, "a live-and-let-live bohemian" who has lots of jobs and lots of boyfriends. Completing the main cast is Mad Men's Zosia Mamet as Shoshanna, who is billed as "a NYU student obsessed with 'women's issues', gluten-free foods and sexcentric self-help".
Dunham and Apatow co-wrote the series alongside Bruce Eric Kaplan (Six Feet Under) and Jenni Konner (Undeclared).