The BBC medical drama was Saturday's most-watched programme, pulling in 6.13m (24.9%) viewers as fans caught their first glimpse of the new-look show.
Saturday night's Casualty episode was an 80-minute special featuring new titles, new cast member Oliver Coleman as Tom Kent and a refurbished Emergency Department following last year's fire.
The episode was also the first to be filmed in Cardiff following the show's move from its long-time home of Bristol.
Casualty's series producer Nikki Wilson today told Digital Spy: "We are thrilled that the exciting new series of Casualty brought viewers rushing into Holby's newly-furbished ED on Saturday night.
"Everybody at Casualty worked really hard to get these new Cardiff episodes off the ground and we're delighted with the positive response."
Casualty's return to screens saw patients flood into the ED in the aftermath of a huge traffic accident.
The show continues on Saturday at 8.40pm on BBC One.
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