'The End of the Line', the opening episode of series 18 focusing on a devastating train crash, was named the winning episode with 18.5% of the vote.
The 2003 episode was written by Ann Marie di Mambro and was the first of a two-parter, which saw Holby's medical staff dealing with the tragic accident. The likes of Martina Laird, Kwame Kwei-Armah, Derek Thompson, Suzanne Packer, Ian Bleasdale and the late Simon MacCorkindale starred in the episode.
In second place with 14.5% was 'Before a Fall', which dealt with Ruth Winters's (Georgia Taylor) suicide attempt. Brenda Fricker's comeback episode 'Nice and Easy Done It' finished in third place with 12.4%.
Series producer Nikki Wilson said: "We're delighted that so many Casualty fans visited the website to revisit their favourite moments of the last 25 years.
"With the series still in great health on its 25th birthday we hope we can keep producing memorable medical moments for many more years to come."
> Watch the Casualty cast discuss their favourite moments
Watch some memorable moments from the chosen episodes in the video below: