The nematode Anisakis simplex (AS) is a world wide distributed parasite that infects consumers of raw or undercoocked parasitized fish. The clinical manifestation of Anisakiosis depend on the site in the digestive tract in which larva lodges. The symptoms develops as a result of the inflammation when the larvae penetrates the gastric mucous. Most of asymptomatic subjects show high levels of specific IgE to AS. Diagnosis of AS allergy is not simple, due to cross-reactivity with other allergens. In childhood is more difficult to make a right diagnosis than in adult population. Most of positive prick test to AS correspond to children with positive prick tests to other allergens. Cross-reactivity between this parasite and other parasites with a higher prevalence in childhood, is the cause of a false diagnosis. The secretor-excretory antigen shows a better specificity, recognizing the true parasitized patients. This antigen could be used as indicator of parasitization. To follow prevention rules AS, avoid consumption of raw fish unless frozen for 48 hours or ingestion of fresh fish always cooked for more than 20 minutes at least at 60 C.