When was the last season of ER?
ER (season 15)
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To mark the end of the series after 15 years, several former cast members make a return to the show. Mark Greene and Robert Romano appear in a flashback episode that explores Banfield's history with County General while John Carter returns to work at County although, unbeknown to his colleagues, he is in desperate need of a kidney transplant. Peter Benton, Doug Ross and Carol Hathaway, Susan Lewis, Elizabeth Corday, Kerry Weaver and Ray Barnett return in various episodes. The series ends with one final multiple casualty incident that brings multiple patients to the ER, and shows that life goes on at County General.