25 year old Adam Schwartz (Joseph Gordon-Levitt) lives a nice and simple life. He has a beautiful girlfriend named Rachel (Bryce Dallas Howard) and works at a museum with his best friend Kyle (Seth Rogen) who complicates his life in annoying but humorous ways.
However, he is soon diagnosed with a rare type of cancer. Considering his young age and healthy lifestyle, Adam has a hard time believing this is happening to him. With no other choice, he decides to start chemotherapy and fight for his life. He breaks the news to his parents, friends and Rachel, who all support him.
To get his mind off of things, Adam begins seeing Katie (Anna Kendrick) a cute 26 year old medical student who is helping him cope with the psychological side effects of chemo. As time goes on and his vitality and health slowly fade, Adam comes to terms with his life and illness. While fighting the cancer he begins to appreciate what he has in life, especially the things he took for granted before his battle.