: To promote the 100th episode, ABC created a real wedding website for Meredith and Derek that fans could actually visit and RSVP to.
: After Derek and Bailey discover that Izzie has an inoperable brain tumor, the group decides to celebrate her life and love immediately. [S5E22] What a Difference a Day Makes
: George O'Malley faces an emotional crisis when almost all the students from the accident die under his care, leaving him devastated until Owen Hunt helps him see the lives he did save. : To promote the 100th episode, ABC created
: Jeffrey Dean Morgan makes a final appearance as Denny Duquette, appearing as a hallucination to Izzie that Derek and Bailey eventually realize is a symptom of her worsening condition. Behind the Scenes Facts : Jeffrey Dean Morgan makes a final appearance
In , the Season 5, Episode 22 milestone titled " What a Difference a Day Makes " is a landmark 100th episode that originally aired on May 7, 2009. It is widely celebrated for its emotional depth, shifting from a planned grand wedding for Meredith and Derek to a poignant ceremony for Izzie Stevens and Alex Karev. The Unexpected Wedding
: As a wedding gift, Derek gives Meredith her first solo surgery—a successful colon surgery overseen by Richard Webber.
: Rhimes described the episode as the moment Meredith evolved from a "dark and twisty" girl into an "extraordinary" woman capable of choosing happiness.