Buffett, a larger-than-life financier known as the "Oracle of Omaha" for his investment savvy, said: "I feel great."
With his big glasses and preference for Cherry Coke, Buffett is known for his humble manner and modest tastes despite amassing billions as the mastermind and chief executive of Berkshire.
In a letter to his company's shareholders, released yesterday after the stock markets closed, Buffett disclosed he had been diagnosed with Stage I prostate cancer last Wednesday and would undergo radiation treatment beginning in mid-July.
Imaging tests revealed no cancer elsewhere in his body, the ebullient 81-year-old investor said.
"The good news is that I've been told by my doctors that my condition is not remotely life-threatening or even debilitating in any meaningful way," he said.
Buffett said that he and his doctors had decided on a two-month treatment of daily radiation, which would restrict his travel "but will not otherwise change my daily routine." "I feel great -- as if I were in my normal excellent health -- and my energy level is 100 percent," he said.
The cancer was discovered during a routine medical check-up that showed an unusually large jump in his blood level of PSA -- a protein that is a prostate-specific antigen produced by the cells of the prostate gland.
The prostate is a small structure, the size of a walnut, that is part of the male reproductive system. "A biopsy seemed warranted," Buffett said.
Prostate cancer is the most frequent cause of death from cancer in men over age 75, according to US official data.
But it is relatively slow-growing compared with other forms of cancer, raising the chances of death from old age or another illness.
"I will let shareholders know immediately should my health situation change," Buffett said. "Eventually, of course, it will; but I believe that day is a long way off," he said. Berkshire shares rose 1.4 percent Tuesday but were down 1.8 percent in post-market trading.