"He received a liver transplant because he was ... the sickest patient on the waiting list at the time a donor organ became available," Dr. James D. Eason, chief of transplantation at Methodist University Hospital Transplant Institute in Memphis, said in a statement late Tuesday. "Mr. Jobs is now recovering well and has an excellent prognosis."
Eason said in a news release posted on the hospital's Web site that when Jobs received the transplant, he was in end-stage liver disease.
The doctor made the disclosure with Jobs' permission. Jobs has been on a medical leave since January.
Eason did not reveal when the operation took place, citing patient privacy. However, The Wall Street Journal reported it was two months ago.
Apple did not confirm the newspaper's report, and has said only that Jobs is looking forward to returning to Apple — which he started in 1976 — at the end of June.
Eason said the hospital could not reveal further information on the specifics of the transplant.
"That's all that we are giving out at this time," hospital spokeswoman Ruth Ann Hale told The Associated Press.
Wall Street has grappled with the implications of Jobs' health since August 2004, when investors learned the CEO had kept a cancer diagnosis secret until after he underwent surgery. The company's past silence on matters of Jobs' health made shareholders jittery when he appeared increasingly, even alarmingly, thin last year.
Investors sent the stock tumbling 5 percent to its lowest point in a year on a rumor last October that Jobs had suffered a heart attack.
Then shares slipped 2 percent in December when Apple said that Jobs would not speak as usual the next month at the annual Macworld conference, then bounced up 4 percent on Jan. 5 when Jobs explained his weight loss as a treatable hormone imbalance. They sank 7 percent a week later after Apple said he would be taking six months off because his medical problems were more complex than he initially thought.
Since then, Wall Street's whiplash has had time to heal, especially because Apple's stock has weathered the recession better than those of most of its competitors.
Cupertino, California-based Apple put Tim Cook, its chief operating officer, at the helm during Jobs' absence.
Apple shares were up 99 cents at $135 in premarket trading Wednesday. They are up more than 70 percent from their 52-week low of $78.20 on Jan. 20.