The fourth series of the British medical drama television series Holby City commenced airing in the United Kingdom on BBC One on 9 October 2001, and concluded on 1 October 2002. The episode run for this series was actually commissioned for 26 episodes, however a further 26 episodes were given the go ahead and were bolted onto the end of Series 4 resulting in a 52 episode series run. In essence, it is a combination of two separate series, but classed as one. From here on, each series was commissioned as a full 52 episode run.