Pat Skinner knew she would be in some pain after her operation - doctors told her it was to be expected.
Mrs Skinner's X-ray clearly shows the scissors in her abdomen
But she was still suffering 18 months later - and an X-ray of her abdomen showed a pair of scissors almost seven inches long had been left inside her.
The 69-year-old, from Sydney, Australia, is now seeking compensation from the St George Hospital, Sydney, where the operation took place.
The hospital has apologised to Mrs Skinner for the mistake.
'Kicked by steel-capped boots'
Mrs Skinner went into hospital for an operation in May 2001 to have part of her colon removed because doctors feared polyps growing there could be cancerous.
But the polyps were benign, and when she was discharged, she was given a clean bill of health by doctors.
Mrs Skinner told the Australian Broadcasting Corporation she had suffered some discomfort after the operation.
"The pain went for a while and then I started to get pains back again, a different type of pain.
"We were going over a bump in the car and I'd be screaming."
Mrs Skinner could not sit or lie down without being in extreme pain, but doctors continued to tell her it would take time for her to recover.
She was even put on anti-depressants and given counselling.
Eventually, Mrs Skinner decided she could bear the pain no longer and went back to her GP.
"I said, 'Look, I just feel like I've been in a fight, I've fallen on the floor and somebody's been kicking me with steel-capped boots'."
She added: "I think my tailbone is crumbling."
'We can only sympathise'
For the first time since she began complaining of her pains, doctors decided to send her for an X-ray.
The scan showed the 6.6 inch (17cm) surgical scissors wedged up against her tailbone.
Pat's husband Don said they were amazed that surgeons had not noticed they had left a pair of scissors inside her.
"How can you not see them? And if you haven't seen them, doesn't someone look around and say, 'Um, where's the scissors gone?'"
Mrs Skinner had to undergo a second operation. But tissue had grown over the scissors, meaning surgeons also had to remove her bowel.
David Pearce, chief executive of the St George Hospital, said: "This is the first time an incident like this has happened at St George. We strongly believe it's not indicative of the quality of the surgical services we provide here.
"Our explanation is that it was human error. It's something we're determined to make sure doesn't happen again."
He added: "We understand how the Skinners feel and we can only sympathise with the terrible error we've made."
Mr Pearce said guidelines had been tightened up at the hospital, and surgical teams now had to make an inventory of equipment at the end of each operation.