Sir Richard Hadlee has bowel cancer.
Last month the former cricket all-rounder had a routine, three-year colonoscopy where a tumour was discovered.
He has since had a successful operation to remove it, and has recovered well.
As a safeguard, further treatment in the form of chemotherapy will commence shortly and last a few months.
His wife, Lady Dianne, said Hadlee's expected to make a full recovery over time.
"Our reasons for making this statement are a desire to be transparent, and to prevent the inevitable speculation and incorrect rumours," she wrote.
"I would also request people's understanding and acceptance of our request for privacy while we go through the next few months, both for ourselves and for the extended Hadlee family."
Hadlee has previously been diagnosed with Wolff–Parkinson–White Syndrome, a disorder which caused his heart to beat irregularly.
The 66-year-old previously needed open heart surgery to survive and still takes medication to thin his blood and keep his heart beat regular.
Hadlee's cricketing greatness is easily defined. He secured a world record 431 test wickets by retirement, had been the lynchpin in New Zealand's golden era of the 1980s and brandished a knighthood in his final test.
Few players in the history of the game have carried as much responsibility within an international team.
Hadlee's 17-year test career saw him become the world test wicket record holder against India at Bangalore in 1988. He overtook Sir Ian Botham's 373-wicket mark when Chris Kuggeleijn caught India's Arun Lal in the slips. Hadlee took a wicket with his final ball in a test against England at Edgbaston in 1990 where he was listed on the scorecard as 'Sir Richard'.
His bowling average of 22.29 from 86 tests is among the best in the game. That statistic was complemented by the all-rounder tag, courtesy of 3124 test runs and 27.16.
Hadlee dealt with life in the limelight as much as any New Zealand sportsperson ever has during his playing career. He received the supreme Halberg award twice and was honoured as the sportsperson of the 1980s.
Listen to Sir Richard Hadlee talk to Andrew Alderson about the 1985 'Gabba test:
New Zealand's recent resurgence is tethered to the benchmark of his success.
Hadlee shared his method for dealing with the increased recognition and subsequent pressure with the Herald before the 2015 World Cup.
He prescribed embracing any added attention as expectations mount.
"The recognition is a huge compliment to what you do on the field but it also carries responsibility when you're in the public domain," he said.
Related: Hadlee tribute to groundbreaking 1949 English tour
"If people recognise you, want your autograph or come up for a chat, I believe it's good to give something back. You bring about goodwill for the sake of a minute or two of your time. Alternatively a bad experience multiplies by 10, 100 or 1000 times once it is spread.
He said you deserve privacy when you're in your own house.
"You should be able to do your own thing without worrying about cameras out front Hollywood-style. You're normal people at the end of the day, so still need to be left alone at times.
"However, when you're out on the road you are public property, so come to terms with it. You've got to be careful with your behaviour whether you're watching sport, at the movies, out fishing or at a restaurant."