The somatic products released from ingested larvae of Gymnorhynchus gigas parasitizing fish induce a Th2 response capable of causing allergic disorders. The objective of the present work was to evaluate the prevalence of anti-Gymnorhynchus gigas antibodies in a Spanish population and established a possible relationship with fish consumption habits. We studied 305 residents in Madrid, with neither clinical symptoms suggestive of gastrointestinal or allergic disorders, nor pathologies related to ingestion of fish that could cause disease. Specific antibody levels were measured by ELISA: 11.8%, 20%, 15.7%, 21%, and 7.5% of the total studied sera were IgA, Ig's, IgG, IgM, and IgE positive, respectively. Seropositivity was not more prevalent among fresh fish consumers and did not increase with frequency of fish consumption. IgE values were lower in the group that never ingested smoked fish. Anti-G. gigas antibody levels were higher in the group that reported frequent consumption of marinated fish. The use of cooking methods with the least heating efficacy (frying, or frying in batter, and microwaving) did not affect seropositivity percentages among consumers. Infection with live plerocercoids is not necessary for seropositivity, and the antibody production, in this case, is due to the absorption of antigens from the parasite following the digestion process. The human health risks of allergic reactions due to parasite antigens remain active after freezing the fish.