Brutal, no-holds-barred fighting should be banned, say doctors in Britain.
Cage fighting is gaining in popularity
The British Medical Association, which has campaigned since 1982 for a ban on boxing, has now turned its attention to extreme mixed martial arts.
Doctors are not calling for a ban on sports such as karate, but instead want to see the end of "brutal" events like cage fighting.
It comes ahead of an ultimate fighting event in London. Organisers said injuries were worse in other sports.
Mixed martial arts is a combat sport in which a wide variety of fighting techniques are used, including striking and grappling.
Events such as the Ultimate Fighting Championship, which is being held at the O2 arena in the capital on Saturday, pits different fighting styles against each other in caged rings.
It emerged in the US during the 1990s and has proved popular on pay-per-view television.
Organisers have now started arranging events in Europe and this has prompted the BMA to speak out.
Dr Vivienne Nathanson, head of science and ethics at the BMA, said: "Ultimate fighting can be extremely brutal and has been described as 'human cockfighting'. It can cause traumatic brain injury, joint injuries and fractures.
"This kind of competition hardly constitutes a sport - the days of gladiator fights are over and we should not be looking to resurrect them.
"As doctors we cannot stand by while violent fighting tournaments are allowed to take place.
"Large amounts of money can be earned by participants, promoters and others linked to ultimate fighting, but no amount of money can compensate for permanent brain damage and premature death.
"As a civilised society we should be campaigning to outlaw these activities."
The BMA said there had been only one reported death in mixed martial arts since it emerged in the early 1990s.
But doctors said this should be put into context as the tournaments are still in their infancy compared to boxing.
However, Paul Griffin, of the British National Martial Arts Association, who has members which take part in mixed martial arts, said: "The issue is being sensationalised.
"There are strict rules governing these fights and there is a good safety record.
"But the bottom line is that people have a choice over whether they take part, they should not be dictated to."
A spokesman for the Ultimate Fighting Championship said the allegations were "absolute nonsense".
"There have been no serious injuries in the history of the Ultimate Fighting Championship. The worst case there has been was a broken arm.
"Sports such as rugby, Formula One and horse riding have more injuries. The death in 1998 was little more than an organised bar fight, it was not an Ultimate Fighting Championship bout.
"There are stringent rules in our fights and we have doctors on the sidelines. The BMA criticism is without foundation."