<b>Background: </b>The prevalence of allergy to fruits and vegetables increased with pollinosis over the last 10 years. So far, clusters of hypersensitivity have been established and corroborated by the molecular characterization of individual cross-reacting allergens. Several case studies demonstrated the existence of allergic reactions to fruits of the subfamily Prunoideae (apricots, cherries, plums and peaches). Here, we present the characterization of a major allergen in cherry. <b>Methods:</b> Characterization was performed using IgE immunoblotting and immunoblot inhibition, N-terminal sequencing, mass spectroscopy analysis and PCR-based cDNA cloning. <b>Results:</b> A 23-kD protein was identified as IgE-binding component. As all cherry-extract-reactive sera displayed IgE-binding to this band, it was designated a major allergen from <i>Prunus avium</i> (Pru a 2). Sequencing the corresponding cDNA identified Pru a 2 as a thaumatin-like protein belonging to the group 5 of pathogenesis-related proteins. <b>Conclusions:</b> A thaumatin-like protein in cherry has been identified as a major allergen (Pru a 2). Homologous proteins from the thaumatin family share sequence similarities and should therefore be checked for the capability to elicit an IgE-mediated allergic reaction.