I have never been able to tell the difference between Mary-Louise Parker and Elizabeth Perkins. It really confused me when I realized they were both on Weeds.
Brian Cox and Albert Finney are also indistinguishable to me.
){kind=link}
For me, it’s David Keith and Robert Wuhl.
And since nobody else has mentioned it yet, Dave Foley and Isabella Rosselini. Of course, it’s easier to tell them apart now that Dave has gray hair and a goatee.
Or is that Isabella?
Mimi Rogers and Jami Gertz
Margaret Colin and Elizabeth Perkins… Can’t tell them apart to save my life.
Reese Witherspoon and Kirsten Dunst
I thought it was Drew Barrymore.
No one has mentioned them yet, but surely I am not the only one!! For me it is Glenn Close and Meryl Streep. I cannot keep the two straight.
I was rewatching Hellboy the other day and I thought the character Liz, played by Selma Blair was actually Zooey Deschanel (who played Trillian in HHGttG)
Morgot Kidder
Elmari Wendel
Carrir fisher
Karen allen
Jan Hooks
I always thought these 5 could be sisters
Sadly i think all but one are now dead.
Oh and i definitely agree with the statement about
Caitlin Clarke and Maura Tierney
When News Radio first aired, i was convinced they were the same person.
I’m a little faceblind so Harper’s Island was as confusing as all get out. All those thin blonde actresses.
You can’t tell me the husband in the Jake from State Farm commercial wasn’t Vince VaughnI.
Nina Dobrev and Victoria Justice are almost interchangeable.
Jeff Daniels and Jeff Bridges.
Thandi Newton and Zoe Saldana are both gorgeous - and get mistaken for each other!
Chris rock and Chris tucker …they play the same roles in movies the motormouth smart ass …and their voices sound the same
Jeff Bridges and Kurt Russell.
Jan Smithers and Pam Dawber.
Chris Evans and Chris Pine.
Keith David and David Keith 
Brad Pitt and Benecio Del Toro have been slowly moving toward convergence over the last couple of decades. In another twenty years, they may well be totally indistinguishable from each other.
Anna Friel and Haylay Atwell. Maybe they’re both just English brunettes, but I can barely tell them apart.
Jane Levy and Emma Stone are both adorable redheads (usually)who play “spunky” really well. They could be sisters.
Years ago, Elizabeth Banks had a small part on Modern Family as a crass, party girl type. I was so distracted by trying to determine if it was EB or Chelsea Handler that I missed the whole point of the storyline.