Apple Inc.'s Steve Jobs said the board has granted him medical leave in order to concentrate on his health.
Apple's stock fell as much as 7 per cent on the Frankfurt Stock Exchange following the news.
"At my request, the board of directors has granted me a medical leave of absence so I can focus on my health. I will continue as CEO and be involved in major strategic decisions for the company," Jobs said in a letter.
During his leave of absence, Chief Operating Officer Tim Cook will be responsible for day-to-day operations, the CEO said in a statement.
Jobs did not specify for how long he would be on leave but said that he hopes "to be back as soon as I can."
Jobs had stepped away from his duties in January 2009 for health reasons, although he remained involved in important issues whilst Cook took over day-to-day operations.
Jobs, a pancreatic cancer survivor, underwent a liver transplant while on leave, returning to the company in late June.
Apple is due to report its fourth quarter results after the markets close on Tuesday.