Previous studies have demonstrated a high prevalence of seropositivity to the Ani s 1 protein in dyspeptic patients with Helicobacter pylori infection, but it is not known whether this represents episodes of anisakiasis misdiagnosis or previous exposure to the parasite without clinical relevance. To investigate the clinical significance of seropositivity to the Ani s 1 protein, a cohort study was performed with 87 consecutive dyspeptic patients who were treated for H. pylori infection. Fourteen (16.5%) patients were seropositive for the Ani s 1 protein, which was associated with the consumption of uncooked fish (p 0.0002). There were no differences in histological findings between subjects seropositive or seronegative for Ani s 1, but seropositive patients had increased eosinophil and basophil leukocyte counts (p < 0.05). Anti-Ani s 1 IgE was associated with a lack of improvement in the group of patients with non-ulcer dyspepsia after successful eradication of H. pylori (p 0.016). Thus, in at least a subset of patients with H. pylori infection, seropositivity to Ani s 1 could have clinical relevance. In addition, these data highlight that only anisakiasis associated with severe allergic or gastric symptoms is currently being diagnosed.