Holby City was created by Tony McHale and Mal Young as a spin-off from the BBC medical drama Casualty, which is set in the emergency department of the fictional Holby City Hospital. Young wanted to explore what happened to patients treated in Casualty once they were taken away to the hospital's surgical wards. While Casualty's scope is limited to ''accident of the week'' storylines about patients entering hospital, Holby City allowed the possibility of storylines about long-term care, rather than immediate life and death decisions. The series was commissioned by BBC One Controller Peter Salmon, and began airing on BBC One on 12 January 1999.

What's the best answer to this question: are holby city and casualty set in the same hospital?
yes