Wendy Dempsey says she drove home with the needle in her back
A woman who received treatment for a long-term back problem arrived home with a 2in (5cm) needle still in her back, she claims.
Wendy Dempsey, 54, said she attended St Woolos hospital in Newport where she was given acupuncture treatment by a physiotherapist on Wednesday.
After leaving the hospital, Ms Dempsey says she drove home to Llanmartin in "agony" with her nephew in the car.
Gwent Healthcare NHS Trust has offered apologies and said it will investigate.
Ms Dempsey said she has submitted a formal complaint to the trust.
"I drove the five or so miles in absolute agony, and had to take painkillers after arriving home," she said.
"Obviously, by driving I was sitting back and pushing the needle in further," she said.
Still in pain, Ms Dempsey said she asked her eight-year-old nephew to look at her back. He screamed, she said, after seeing the needle sticking out.
Ms Dempsey says she then called her doctor who recommended she return to the hospital to have it removed.
Mrs Dempsey had this picture taken of the needle in her back
"My next door neighbour had to drive me to the Royal Gwent - and I had to sit on my side," she added.
Ms Dempsey said: "I'm not prepared to let it go."
A spokesman for Gwent Healthcare NHS Trust said: "We have spoken to Mrs Dempsey and have offered our sincere apologies.
"She has made a complaint which will be fully investigated by the trust.
"We operate strict protocols for the use of acupuncture and we will contact her as soon as our investigations into this incident are complete," he said.