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.
Dr. Bailey (Chandra Wilson) and Dr. Meredith Grey (Ellen Pompeo) are the same age in real life.