In the print menu, be sure that scaling is set to "none".
If that isn't the cure, you'll need to give us a few more details to help like, what application and version you are talking about, what type of file (if not a PDF), OS...etc. The more info, the better chance of getting help.
this is a pdf file. and that didnt make any changes in my document?
Ca you post a sample of the file? I ask because the only thing in Reader that will reduce or enlarge the scale would be the setting that I mentioned. I would suspect that the image isn't the exact size in the PDF that it was elsewhere (before it was a PDF) and is printing at the correct size.