A woman battling ACC for entitlements was described by case managers as "completely deranged" and a "pain in arse person" in internal emails.
Auckland amputee Diane Smith discovered the comments after requesting her file from the Accident Compensation Corporation.
Mrs Smith, 54, fell on a cafe's broken steps in 2003, fracturing her left ankle and dislocating her knee, and six years later her lower leg was amputated following problems with a screw and plate inserted to repair her ankle.
She also developed shoulder problems after a long period using crutches.
The emails show ACC staff mocked Mrs Smith's requests for assistance, and one case manager called her claim "a NIGHTMARE!!", while another wrote in March 2008: "This woman is completely deranged".
Mrs Smith said the comments were "disgraceful".
"When you've got people treating you like you are a [bludger], they forget I had a major accident and I had a medical misadventure.
"I didn't ask to have an accident. You pay your taxes and your ACC levies to take care of you if something happens."
Even before viewing her file, she was given an apology by ACC team leader Lynne Flood - the third she had been given in four years, The New Zealand Herald reports.
"A few emails between ACC staff are not written to our required standards of professionalism and which you may find upsetting," Ms Flood wrote.
She said ACC was investigating and was working to improve its communication standards.
Mrs Smith has previously received apologies from ACC for failing to treat her with dignity and respect, and for failing to communicate honestly, openly and effectively, after battling for years for entitlements, including housing modifications and a new vehicle.
It's another embarrassment for ACC, just weeks after revelations that sensitive data about thousands of clients was accidentally sent to ACC claimant Bronwyn Pullar, in a saga that sparked a series of investigations and led to the resignation of former ACC minister Nick Smith.