"I love Apple so much and hope to be back as soon as I can," Jobs said in an e-mail to employees that was released by the company. "In the meantime, my family and I would deeply appreciate respect to our privacy."
Jobs plans to continue to hold the title of chief executive, but will limit his responsibilities to being involved in "major strategic decisions for the company."
Chief Operating Officer Timothy Cook will be responsible for all of Apple's day-to-day operations. Cook was appointed interim CEO in 2009, when Jobs was on leave the first half of the year. During that time, Jobs underwent a liver transplant, stemming from a rare form of pancreatic cancer that forced the CEO to take a medical leave in 2004.
The tone of Jobs' latest announcement is different than it was in 2009, when he said he would return in June. This time, no date was given for his return, with Jobs saying only that he "hoped to be back as soon as I can."
Such uncertainty could have an impact on the company's stock. Many investors see Jobs as the genius behind the company's innovations, and credit him with its resurgence over the past decade. Jobs led with the iPod in 2001 and more recently with the iPhone and iPad. From the time speculation of Jobs's health surfaced in the second half of 2008 through his leave of absence and return in July 2009, the company's stock price fell 23.3%.
Apple has refused to publicly discuss definitive succession plans if Jobs was to leave the company permanently, saying such disclosure would provide inside information that could be used by competitors. Some analysts believe Cook would be the logical choice, given the praise he received from Wall Street, Jobs and Apple's board, for his work as interim CEO in 2009.
"He's proven himself as being very capable in that role, and yes, he would be the logical choice," Michael McGuire, analyst for Gartner, told InformationWeek.
Cook joined Apple in 1998 from Compaq, where he was vice president for corporate materials. He became Apple COO in 2005, after serving as executive VP of worldwide sales and operations. Cook's "outstanding performance" as interim CEO in 2009 led to the company giving him a $5 million bonus, while also receiving a salary of $800,000 and a stock award valued at $52.3 million for the 2010 fiscal year, according to documents filed with the Securities and Exchange Commission.
While investors are jittery over Apple's future, if Jobs was to leave, the company is seen by some as having a strong executive team capable of maintaining the company's momentum as a market innovator.
"The hallmark of a very good chief executive is to be able to put a team together that operates well in his absence," McGuire said. "I don't think Jobs gets enough credit for doing that."
Apple is expected to address Jobs' medical leave on Tuesday during a conference call with analysts following its release of first quarter results.