[pdftex] pagebackref

[Ronaldo Cristiano Prati]

Maybe it's a beginner question, but there is no matter that I can do it
work.

I'd like to add back's ref in the bibliography. So, I turn on the
pagebackref option in the hyperref package. I'm using this command

\RequirePackage[colorlinks=true,
                linkcolor=blue,
                citecolor=blue,
                a4paper,
                pdftitle = {},
                pdfsubject = {},
                pdfkeywords = {},
                pdfauthor = {},
                pagebackref,
                pdftex]{hyperref}

But the page numbers don't appear in bibliography. What am I doing wrong?
I using the chigago bibliography style and miktex. The package chicago was
loaded before the hyperref package.

Tanks