Steven P. Jobs, the co-founder and chief executive of Apple, is taking a medical leave of absence, a year and a half after his return from a liver transplant, the company said on Monday.
Mr. Jobs announced his leave in a letter to employees, saying he was stepping aside "so I can focus on my health" but would continue to 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 D. 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," Mr. Jobs said in the message.
Mr. Jobs recovered from pancreatic cancer after surgery in 2004, but has continued to be plagued 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. While he was energetic and exhibited his unique brand of salesmanship as he unveiled new products during 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, 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 on Monday, Mr. Jobs said, "My family and I would deeply appreciate respect for our privacy."
During his prior leave, Apple kept details of Mr. Jobs's health private, prompting criticism among some shareholders who contended that the company had an obligation to be more forthcoming with information.
Apple's stock immediately dipped on foreign exchanges Monday, falling 6 percent in Germany. Monday is a market holiday in the United States.