An outbreak of trichinellosis occurred in Izmir, Turkey, between January and March 2004. The outbreak was caused by the consumption of raw meat balls made of beef deceptively mixed with pork infected with Trichinella britovi. A total of 1098 people who had consumed this food either in 14 restaurants or from the street vendors located in three different neighbourhoods, consulted six different healthcare centres with a wide range of clinical signs and symptoms. Of them, 418 (38.1%) patients fulfilled the criteria for the diagnosis of acute trichinellosis. The most commonly observed signs and symptoms were myalgia (89.2%), arthralgia (69.9%) and eyelid (67%) and facial oedema (65.8%). High levels of creatinine kinase (69.3%) and lactate dehydrogenase (93.8%) with leucocytosis (> 10 000/mm(3), 58.9%) and eosinophilia (> 1000/mm(3), 60.5%) were the most prominent laboratory findings. All, but 13 of these patients were treated with mebendazole or albendazole. Based on the physicians' assessments of disease severity, 78 (19%) patients were additionally given prednisolone in whom a significantly more rapid recovery of clinical signs and symptoms (e.g. fever, myalgia, facial and eyelid oedema) was observed, with a rapid improvement in leucocytosis, eosinophilia and muscle enzymes, compared with those, who had not received corticosteroids (P < 0.05). Beef illegally mixed with pork of unknown origin, by a wholesale butcher who had sold this product to restaurants and street vendors at a lower price than the prevailing market price of beef, was the cause of this large-scale outbreak in a country with a predominantly Muslim population.