HTML appearing div makes a scrollbar appear

I have a webpage with a layer that appears which has height 500px. Inside this layer I have a normal webpage that has a hidden div. On clicking on a link in this layer this div appears, but a scrollbar in the layer appears too. I would like that the appearing of this div doesn't make the scrollbar appear, that is, this div simply appears over the page...

I hope I've been clear, it's really hard to explain.

Thanks all

EDIT:

I cannot post the code of the page because it's more than 800 lines long.

I try to explain myself a bit better: I have this page full of text with in the middle a h开发者_运维知识库idden div. Of course when the visibility = block is set for this div, it appears right where I want, but since it's in the middle the page becomes "longer" and an overflow appears, and overflow: hidden doesn't do the job :(.

Not sure exactly what you mean, but won't overflow: hidden do the job?