CUPERTINO, Calif. -- Steven P. Jobs, the co-founder and chief executive of Apple Inc., is taking a medical leave of absence, a year and a half after his return from a liver transplant, the company said Monday.
Mr. Jobs announced his leave in a letter to employees, saying he was stepping aside "so I can focus on my health," but still would be involved in major strategic decisions at the company.
"I love Apple so much and hope to be back as soon as I can," Mr. Jobs said.
As during his prior medical leave in 2009, Timothy Cook, the company's chief operating officer, will run day-to-day operations, Mr. Jobs said.
"I have great confidence that Tim and the rest of the executive management team will do a terrific job executing the exciting plans we have in place for 2011," he said in the message.
Mr. Jobs recovered from pancreatic cancer after surgery in 2004, but he has continued to be beset by health issues. In January 2009, Mr. Jobs went on a medical leave. During the leave, Mr. Jobs secretly flew to Tennessee for a liver transplant.
In June, 2009, Apple said Mr. Jobs was back at work, and he reappeared in public for the first time in September of that year.
Although he was energetic and exhibited his unique brand of salesmanship as he unveiled products during the 90-minute event, he continued to look gaunt. Since then, Mr. Jobs has headlined a string of product introductions, including the iPhone 4 and the iPad and a new line of MacBook Air laptops, where he was equally energetic and focused, but still looked frail.
At one such event in July, 2010, a reporter asked Mr. Jobs about his health, and he replied, "I'm feeling great."
In recent months, he has looked increasingly frail, according to people who have seen him.
In his message to the staff yesterday, Mr. Jobs said, "My family and I would deeply appreciate respect for our privacy."
During his prior leave, Apple kept details of Mr. Jobs' health private, prompting criticism among some shareholders who contended the company had an obligation to be more forthcoming.
Mr. Jobs suffers from immunesystem issues common with people who have received liver transplants and, as a result, his health suffers from frequent "ups and downs," according to a person with knowledge of the situation, who agreed to speak on condition of anonymity because he was not authorized to discuss it.
In recent weeks, Mr. Jobs began a down cycle and slowed his activities at Apple, the person said.
Mr. Jobs has been coming to the office about two days a week, rather than daily, and appeared increasingly emaciated, the person said.
He frequently lunched in his office rather than in the company cafeteria, the person said.
An Apple spokesman, Katie Cotton, said Apple would have no further comment beyond Mr. Jobs' statement.
Apple's stock immediately dipped on foreign exchanges, falling 6 percent in Germany.
Financial markets in the United States were closed Monday in observance of Martin Luther King's birthday.