Lesh, 66, writes he will have his prostate surgically removed in December.
"Since we caught it very early and it's small and slow-growing, I fully expect to have a rapid and complete recovery," he said.
The California native, who has been touring with various musicians under the banner Phil Lesh and Friends, said he was "feeling energetic as always" and no scheduled tour dates would not be impacted.
Lesh had a liver transplant in 1998 as a result of complications from hepatitis C and has been an outspoken advocate of organ donation programs.
Notable deaths of 2014 [PHOTOS]
Polly Bergen, Emmy Award-winning actress, dies