Martha Plimpton

Parenthood will be trying for Martha Plimpton, who has been cast on Grey's Anatomy as the mother of a sick young patient.

Fall TV: See what's on and when

Plimpton will appear in multiple episodes, starting with the two-hour season premiere airing Sept. 24, an ABC rep confirms.

As reported first by TVGuide.com, X-Files alum Mitch Pileggi will also guest-star in the sixth-season opener.

Plimpton's previous TV credits include Law & Order: SVU (for which she earned an Outstanding Guest Actress Emmy nod) and a 1999 run on ER. On the big screen, she has been in such films as Beautiful Girls and Parenthood, where she played daughter to Dianne Wiest and girlfriend to Keanu Reeves.