Even without Clooney, ER's swan song pulled in 16.2 million viewers, its largest audience in several years.
The two-hour series finale brought some familiar faces back to the ER, including former series regulars Eriq La Salle, Sherry Stringfield, Laura Innes and Alex Kingston. Those actors, along with Julianna Margulies and current cast members, also contributed to a one-hour retrospective that aired before the finale.
In a nod to ER's beginnings, the final episode had the daughter of original character Mark Greene (Anthony Edwards) deciding to follow in her father's footsteps and become a doctor.
ER debuted on NBC 15 years ago and became an instant hit with both viewers and critics.