It's not the films. The quality, he said, is better than ever. It's the size.
"I'm starting to hear some negative comments about how crowded it is and how difficult it is to get from venue to venue when there's traffic and people in the streets and so forth," Redford said. "We're going to have to look at that."
Redford still seems somewhat bemused that the Festival grew the way it did over the past three decades. He sees it as a combination of the narrowing of the entertainment business -- when filmmakers and actors had to look outside of Hollywood to find material and projects worth doing -- and a product of globalization.
"When actors came who were well known, then the paparazzi came. Then once the paparazzi came, the fashion houses came. Suddenly this thing was going haywire," he said, laughing that the recession actually helped temper the frivolousness a bit.
But people continue to turn out in droves, looking to be among the first to see a breakout filmmaker's debut -- like Ryan Coogler's "Fruitvale Station" or Damien Chazelle's "Whiplash."
"As it grew, so did the crowds, so did the development in Park City. Well, at some point, if both those things continue to grow, they're going to begin to choke each other," Redford said. "So then I have to think about, oh, do we now risk being who we are in the first place? Do we risk (losing) the heart and soul of what we were when we started against the odds. ... Do we have to now rethink things?"
Ideas are already swirling in Redford's brain about how the Festival can and should evolve.
"You have a couple of choices. You can go hard and say we're going to stop it. Say 'that's the end.' Let it go. Let someone else do it," he said. "Or, you say well, if you want to keep it going, we can't keep it going the way things are."
One thought Redford had was to break up the festival into sections, instead of cramming narrative, documentaries, shorts and everything else into a tight 10 days in January. So, in this scenario, narrative features could play in January, and February would be for documentaries.
"I don't know whether that works or not," Redford acknowledged. "That's just an idea that's worming in my head."
The Sundance Film Festival wraps on Sunday.