A south Wales health board has been placed in special measures because patients have been waiting nine months for surgery.
Anuerin Bevan Health Board has been told that it is "not acceptable" for patients to wait over six months.
Health Minister Edwina Hart told AMs "swift and decisive action" had been taken.
The board confirmed it had been censured for its unacceptable waiting lists.
Mrs Hart revealed that the health board has been placed in special measures in answer to a question from Conservative AM for Monmouth Nick Ramsay on Wednesday.
He said one of his constituents had to wait over nine months for a knee replacement operation, whereas similar surgery for patients over the border in England was taking "a matter of weeks".
Assembly government targets say patients should start hospital treatment within 26 weeks of being referred by their GP.
The maximum waiting time allowed is 36 weeks.
The minister told AMs: "I have made it quite clear to the Aneurin Bevan Local Health Board that it is not acceptable for patients to wait more than six months.
"Senior officials have had meetings with the board to ensure that swift and decisive action is taken, and we have placed the health board under special measures in this regard.
"We have also ensured that the health board has developed comprehensive plans to deal with the issues.
"We are aware that it is waiting to appoint four senior orthopaedic surgeons, and it expects to treat all orthopaedic patients within the maximum waiting time by March 2011.
"It is incumbent on me to keep an eye on that, to make sure that it delivers in that respect."
The Aneurin Bevan Health Board came into being in October 2009, replacing the former Gwent Healthcare NHS Trust and the Blaenau Gwent, Caerphilly, Monmouthshire, Newport and Torfaen Local Health Boards.
The board delivers services to 600,000 people. Last week it oped the Aneurin Bevan hospital on the site of the old steelworks in Ebbw Vale.
The £53m hospital is the first in Wales' to offer every patient their own room.
A spokesman confirmed the Aneurin Bevan Health Board has been placed on special measures because of unacceptable waiting lists.
In a statement, the board said: "We have been working with the Welsh Assembly Government's delivery support unit since July 2010.
"While this is not an issue about standards and quality of service, we very much welcome the additional support they have provided to help us develop local plans to achieve the orthopaedic access target."