They have highlighted a condition called anisakiasis which comes from eating undercooked or raw fish
Sushi-lovers are being warned about the dangers of parasites from eating raw and undercooked fish.
Doctors writing in the British Medical Journal say the growing popularity of the dish has seen a rise in parasitic infections.
Raw fish can carry parasitic worms, which are able to invade the stomach wall or intestines of humans.
Experts treated a 32 year man in Lisbon who was found to have a parasite in his gut which had to be removed using a special kind of net.
An endoscopy later revealed the cause of the problem: the larvae of a type of parasitic worm from the genus Anisakis.
They noted that the condition, known as anisakiasis, is caused by eating undercooked or raw fish or seafood that has been contaminated. The patient later revealed that he had recently eaten sushi.
Writing in The British Medical Journal a doctor said that when it comes to anisakiasis "Most of the cases were described in Japan due to food habits; however, it has been increasingly recognised in western countries.
The author pointed to a Spanish study that reported 25 cases of the condition over a three year period from 1999 to 2002.
An Italian study also advised that medical professionals should suspect the condition should patients complain of severe abdominal pain after eating raw fish, pointing out that "no effective pharmacological treatment is able to kill the larvae once eaten."