Show all categories

I want to show all of the categories – not just the ones I’ve posted in – using the wp_list_cats function, so I’ve done this (which I’m pretty sure is right, according to the Wiki):

wp_list_cats(‘optionall=1&optioncount=1’);

But for some reason it’s still only showing the categories I’ve posted in. I also tried optionall=0 just in case I’m particuarly blind, but changing that variable doesn’t seem to do anything.
Any help will be appreciated,
Liam.