It will be only the second time since 1959 that Nicklaus has missed The Masters. He also skipped in 1999 when he was recovering from hip replacement surgery.
While Nicklaus, 62, has expressed concerns about competing against players half his age on an Augusta National course that has added nearly 300 yards, it was a back injury that has plagued him for nearly a year that forced him to withdraw.
Nicklaus also withdrew from this week's Legends of Golf on the Senior Tour.
'I have tried over the last couple of months to get my body and my golf game in shape to play at the Legends and possibly The Masters,' Nicklaus said. 'And while encouraged, I made a decision today that neither is at the point I hoped they'd be at this stage.
'I do not think my golf game is suitable right now for the competition.'
He has not played an official tournament since July 29, when he tied for third in the Senior British Open.
'We are disappointed that due to his health, Jack will not be competing in this year's Masters,' Augusta National chairman Hootie Johnson said. 'Jack has made numerous contributions to this tournament, and we hope physically he is able to play golf again soon.'
Nicklaus said he will continue a fitness program designed to help his back. He hopes to play in the Tradition, the first major on the Senior Tour to be played the last week in April in Arizona on a course he designed.
'My back is better, and hopefully it will come around to the point where it will allow me to play golf in the not-so-distant future,' he said. 'I really miss competitive golf. It's in my blood, and I very much look forward to playing again soon.'
He first suggested he might skip The Masters in January, when his lower back caused problems swinging the club.
Nicklaus joined Augusta National last year and played in a members' tournament in November. He said he couldn't reach the fairway bunker on No. 1 from the members' tees, and routinely hit his drives only about 210 yards.
Golf World magazine recently checked the scores Nicklaus was posting at his home course, The Bear's Club in Jupiter, Fla., and found his handicap index was 2.
Nicklaus still plans to go to Augusta National next week for the Champions Dinner, and did not rule out playing The Masters again, depending on his health.
His six victories, the last one coming in 1986 when he was 46, tell only part of the story of how Nicklaus dominated Augusta National with power, skill and experience in 42 appearances in The Masters.
When he missed the cut last year at age 59, it was only the fourth time he failed to make it to the weekend at golf's first major championship. He also missed the cut in 1994, withdrew in 1983 and missed the cut as an amateur in 1959.
He won his first Masters in 1963 and became the first back-to-back champion in 1965-66. In the 1965 Masters, Nicklaus set the tournament record of 271 with a nine-stroke victory over chief rivals Arnold Palmer and Gary Player.
The record was tied by Raymond Floyd in 1976, and broken by one stroke when Tiger Woods shot a 270 in 1997 during his 12-stroke victory.
The most dramatic victory was his last one, when Nicklaus shot a 30 on the back nine to beat Tom Kite and Greg Norman in 1986.
Even after turning 50, Nicklaus has pulled a few surprises. He tied for sixth in 1998 after another Sunday charge, and in 2000 he was only six strokes out of the lead going into the weekend. He closed with a 81-78 to tie for 54th.
'Needless to say, I have a special place in my heart for Augusta National and The Masters, and I will miss not playing there this year,' he said. 'I am certainly hopeful that I may have the chance to play The Masters in future years.'
Full coverage of the 2002 Masters