|Jason Segel||Peter Bretter|
|Kristen Bell||Sarah Marshall|
|Da'Vone McDonald||Dwayne the Bartender|
|Steve Landesberg||Dr. Rosenbaum|
|Jonah Hill||Matthew the Waiter|
|Jason Bateman||Animal Instincts Detective|
|William Baldwin||Detective Hunter Rush|
Struggling musician Peter Bretter is better-known as the boyfriend of TV star Sarah Marshall . After she unceremoniously dumps him, he feels lost and alone but makes a last-ditch bid to get over it by going to Hawaii. However, she and her new boyfriend are there in the same hotel.