The fifteenth and final season of the American fictional drama television series ER premiered on September 25, 2008, and concluded on April 2, 2009, in a two-hour episode preceded by a one-hour retrospective special.

The producers agreed to film two S15 episodes at the very end of the Season 14 production cycle so that all three actors could finish their time on the show and move on to other projects.

Luka Kovač and Abby Lockhart leave for a new life in Boston, Brenner must deal with issues surrounding his childhood, and he comes to a crossroads in his relationship with Neela, Samantha Taggart and Tony Gates' relationship suffers a major setback after an accident involving Alex Taggart while Neela Rasgotra is forced to make some tough decisions, both personal and professional.

Peter Benton, Doug Ross, Carol Hathaway, Susan Lewis, Elizabeth Corday, and Ray Barnett return in various episodes.

Meanwhile, Abby misdiagnoses a patient, and talks about her plans to leave Chicago to start a new life with Kovač, while Morris must pick up the pieces after Pratt's death.

Meanwhile, Sam's sister (Shannon Woodward) drops by unexpectedly; Gates and Morris treat an elderly man (Rance Howard) who was assaulted on the street; and Brenner is shocked by a patient's diagnosis.

The ER doctors and nurses assist at a camp for children recovering from open heart surgeries where Morris proposes to Claudia and Brenner befriends a kid who does not want to join in with the activities.