It's a big deal.

Saks Fifth Avenue is broadening its target customer base by extending the size runs it carries, particularly in designer brands.

"After recent review, we concluded there are customers who desire designer clothing in sizes that are not currently available in our stores," the company said in a statement to StyleList.

"To meet her needs, Saks Fifth Avenue has worked with certain well-known designers and for Fall 2010 we will offer some designer brands up to size 16 or 18 in select Saks Fifth Avenue locations."

Designer brands often stop their conventional size runs at 10, but will make larger pieces upon request. Consequently, Saks Fifth Avenue offers sizes up to 10 for most collections.

Brands participating in this program are reported to be Chanel, Dolce & Gabbana, Alexander McQueen, YSL, Fendi and Roberto Cavalli.

The department store currently offers plus sizes through Salon Z. And, as we previously reported, that department has already started adding labels like Kay Unger.

In related news, check out what Crystal Renn told us about designing a plus-size clothing line.