The twenty-seventh series of Casualty began airing on BBC One on 18 August 2012 with an episode featuring a disaster at a music festival. Filming series 26 was completed in April 2012 and filming series 27 began a week later. The first episode was in the normal format – a 50-minute episode. This season is 44 episodes, increasing from 42 for the previous one. Viewing figures for the first episode were 5.19 million viewers, continuing to be one of the most watched programmes of a Saturday night.

Casualty is a British medical drama television series that premiered on 6 September 1986 on BBC1. The series was created by Jeremy Brock and Paul Unwin. It is set in the fictional Holby City Hospital, in the equally fictitious city of Holby, and features occasional crossovers of characters and plots with spin-off show Holby City. Casualty follows the professional and personal lives of the doctors, nurses, paramedics, hospital management and patients at Holby General. It features an ensemble cast of regular characters, and began with ten main characters in its first series, including the longest-serving character Charlie Fairhead. They have all since left the series. Many main characters have been written in and out of the series since. In addition, Casualty features guest stars each week, as well as recurring guests that take part in story arcs that span a portion of a series or multiple series.