The fourth series of the British medical soap opera Doctors originally aired between 2 September 2002 and 13 June 2003. It consisted of 154 episodes. An increase in episode output saw an increase in the core cast, with six regulars cast for the series: Laurence Penry-Jones, Ela Kay, Stirling Gallacher, Diane Keen, Seán Gleeson and Ben Jones. Penry-Jones and Kay departed their roles at the end of the series. The series received an average of 2.5 million viewers.

As the episode output for Doctors increased, the core cast increased. The fourth series saw the castings of six regulars. The introductions began with flatmates Oliver Berg (Laurence Penry-Jones), a doctor, and Carolina Shaw (Ela Kay), a receptionist. Oliver became the first regular gay character on Doctors. Stirling Gallacher then joined the series as doctor Ronnie Woodson. She was followed by Ronnie's onscreen husband, lawyer George (Seán Gleeson).

Diane Keen then joined as Julia Parsons, the ex-wife of Mac McGuire (Christopher Timothy). She was asked to join on an initial three-month stint and accepted due to having worked with Timothy before. She then decided to stay on past her first stint. The last regular to be introduced was Greg Robinson (Ben Jones), a doctor. The series saw two regulars depart, with Penry-Jones and Kay departing from Doctors in scenes that see Carolina die in an explosion and Oliver leaving from grief. Guy Burgess was also introduces as Jerry Walsh, a firefighter and love interest for Faith Walker (Eva Fontaine).