Sorry, my installation of SSRS 2008 and even 2008R2 are both long since gone.

In 2016 (so this may not work for you), you go to Parameter Properties.

Check Allow Multiple Values.

Go to Default Values. Choose "Get values from a query".

Select the dataset containing the values.

Then choose the Value field.

When I did it, all the values I set as default were checked.

I suppose if you wanted something other than "ALL" to be selected, then you would have to create another dataset with the defaults and point at that for the default set.

(Testing my light sabre...)

Here's[/url] the article I loosely followed...

<severs hand trying light sabre>... oh well! So much for being a Jedi!