Among the wide variety of tree nuts, walnut is an allergen that deserves special attention in the context of acute allergic reactions, due to their severity, low inducing trigger dose, and minimal likelihood of developing tolerance. The overall consumption of walnut has been steadily increasing, while the importance of this allergen as a trigger for anaphylaxis is underestimated due to its often “hidden” presence in foods and the difficulty of trigger verification. This article presents the epidemiological aspects of walnut food allergy, provides current data on the molecular characteristics and properties of various allergen proteins, and their clinical significance for the development of anaphylaxis. The article is supplemented with two clinical cases of food anaphylaxis to walnuts from own clinical practice.