In the premier screening of the film, 241 people walked out of the theater, including
Rock Hudson who said "Will someone tell me what the hell this is about?"
Arthur C. Clarke once said, "If you understand '2001' completely, we failed. We wanted to raise far more questions than we answered."
There is no dialogue in the first 25 minutes of the movie (ending when a stewardess speaks at 25:38), nor in the last 23 minutes (excluding end credits). With these two lengthy sections and other shorter ones, there are around 88 dialogue-free minutes in the movie.
The movie was not a financial success during the first weeks of its theatrical run. MGM was already planning to pull it back from theaters, when they were persuaded by several theatre owners to keep showing the film. Many theater owners had observed increasing numbers of young adults attending the film, who were especially enthusiastic about watching the 'Star Gate' sequence under the influence of psychotropic drugs. This helped the film to become a financial success in the end, despite the many negative reactions it received in the beginning.
In Chicago, a group of hippies went to the film several times, sitting in the front row until the intermission. Then they would move to the floor in front of the screen to watch the final star ride from the closest possible point.