Miranda Bailey was the only role written with a character description: "tiny blonde with curls".
The character Alex Karev was not in the original pilot script. His role was inserted into the pilot as an afterthought, in order to provide a foil, as well as male companionship for Dr. George O'Malley. Since he wasn't added until after the pilot was shot, scenes with him were either re-shoots or digitally altered.
Kate Walsh's character, Addison Shepherd, was only supposed to appear in five episodes, but Addison quickly developed a fan base, so they kept Walsh on the show.
Every episode shares the name with a song title by a popular artist. Several are named after The Beatles and R.E.M. songs.
Patrick Dempsey auditioned for the role of Dr. Gregory House on House (2004), before taking the role of Dr. Shepherd.