Leno had checked himself into the hospital Thursday after feeling sick. His publicist, Dick Guttman, said doctors found that Leno's illness wasn't "symptomatic of anything serious" and he was released Friday.
Guttman said he couldn't provide details of what ailed the 58-year-old comedian.
NBC said Leno was feeling much better and was "anxious to return to work Monday."
Leno's Thursday and Friday shows were canceled, with reruns taking their place. It was the first time Leno, who took over "Tonight" in 1992, missed a show because of illness.