Almond is one of the tree nuts listed by U.S. FDA as a food allergen source. A food allergen identified with patient sera has been debated to be the 2S albumin or the 7S vicilin. However, neither of these proteins has been defined as a food allergen. The purpose of this study was to clone, express, and purify almond vicilin and test whether it is a food allergen. Western blot experiment was performed with 18 individual sera from patients with double-blind, placebo-controlled clinical almond allergy. The results showed that 44% of the sera contained IgE antibodies that recognized the recombinant almond vicilin, indicating that it is an almond allergen. Identifying this and additional almond allergens will facilitate the understanding of the allergenicity of seed proteins in tree nuts and their cross-reactivity.