This advert was included on a leaflet from the University Hospital Wales
Hospitals in Wales are being told by the health minister to stop handing out leaflets which include advertisements offering help to claim compensation.
Edwina Hart said it is "highly inappropriate" for the NHS to advertise services from personal injury lawyers.
She had written to all NHS trusts about it but was "disappointed" adverts were still used at Cardiff's University Hospital of Wales.
Cardiff and Vale NHS Trust said the leaflet was distributed by mistake.
The health minister was contacted after a patient received an information leaflet at the hospital in Cardiff with advice on exercises for sprained ankles.
But on the back was an advertisement with the headline "Been Injured? Not sure what to do next?"
Plaid Cymru AM Leanne Wood, who was contacted by the patient who lives in her South Wales Central constituency, said: "The advertisement then featured details of a company which provided help in claiming compensation for a variety of incidents including road traffic accidents, a slip or trip or accidents at work."
She said she understood the advertisements were used to subsidise the cost of patient information leaflets.
"But it seems rather odd to me that the Cardiff and Vale NHS Trust should allow advertising along these lines when it could potentially lead to claims against hospitals and encourages the compensation culture," she said.
"I noticed in the trust's annual accounts for 2008-09, that the trust set aside £3.2m as potential liabilities for personal injury claims."
The AM wrote to Ms Hart, who said she had written once again written to Cardiff and Vale NHS Trust to express her "disappointment" that the adverts had continued to appear on leaflets, despite previously being asked to stop them.
The health minister said she had written to all NHS organisations in March 2008 and at the start of this year instructing them to stop using the advertisements to subsidise the cost of patient information leaflets.
"Cardiff and Vale NHS Trust responded to my officials with assurances that they do not use patient information materials containing advertisements by personal injury lawyers," said Ms Hart
"I am, therefore, extremely disappointed to hear that this activity is continuing. I have written to Jan Williams, Chief Executive of the trust, asking her to provide me with an explanation."
A Cardiff and Vale NHS Trust spokesperson said: "The trust fully supports the withdrawal of all patient information leaflets featuring adverts for personal injury lawyers.
"Regrettably, this was an occasion where an old leaflet was still in circulation and given to a patient.
"Immediate checks are being carried out in all areas so that any leaflets featuring adverts for personal injury lawyers are removed and replaced as soon as possible."