In a letter published on the company's Web site, Jobs said he was taking the unusual step in discussing his condition, because of the "flurry of rumors about my health, with some even publishing stories of me on my deathbed."
The latest round of speculation started last month when the company announced that Jobs would not deliver the keynote at the Macworld conference this week. Jobs has given the keynote every year since 1997, so the announcement heightened consternation on Wall Street, which was already nervous over Jobs' mysterious weight loss, first noticed in a conference in June.
Fueling worries was a report on the blog Gizmodo, which quoted unnamed sources saying Jobs was in "rapidly declining" health. The report caused Apple stock to fall. In late-morning trading on the Nasdaq on Monday, Apple stock was up about 4% to almost $95 a share.
Jobs, a survivor of pancreatic cancer, said he decided to discuss his health, so it wouldn't detract from Macworld, which is typically where the company makes some of its most important product announcements for the year. This year's keynote is scheduled to be delivered Tuesday by Phil Schiller, senior VP for worldwide product marketing.
Jobs acknowledged he had been losing weight throughout 2008 and that the cause had been a mystery to his doctors. Jobs decided a few weeks ago that finding the root cause and reversing it needed to become his "No. 1 priority."
"Fortunately, after further testing, my doctors think they have found the cause -- a hormone imbalance that has been 'robbing' me of the proteins my body needs to be healthy," he said. "Sophisticated blood tests have confirmed this diagnosis."
Jobs went on to say that the remedy was "relatively simple and straightforward" and that his doctors believed it would take until late spring to regain his weight. "I will continue as Apple's CEO during my recovery," he said.
"I will be the first one to step up and tell our board of directors if I can no longer continue to fulfill my duties as Apple’s CEO," Jobs said. "I hope the Apple community will support me in my recovery and know that I will always put what is best for Apple first."
In a brief statement, Apple's board said it was firmly behind Jobs' decision to stay on as CEO. "Apple is very lucky to have Steve as its leader and CEO, and he deserves our complete and unwavering support during his recuperation. He most certainly has that from Apple and its board," the statement said.
Besides announcing Jobs won't deliver this year's keynote, Apple last week also said it would no longer participate in Macworld after this year. The decision has left the future of the trade show in doubt. Macworld is run by technology publisher and event manager IDG, which has said the show will continue without Apple.