The twelfth series of the British medical drama television series "Casualty" commenced airing in the United Kingdom on BBC One on 11 September 1997 and finished on 28 February 1998. The first episode was originally due to be shown on the evening of Saturday 6 September, but this was delayed until the following Thursday due to coverage of the Funeral of Diana, Princess of Wales earlier on that day, as the BBC felt it would be inappropriate to air the episode so soon after such an event.