Eosinophilic esophagitis (EoE) and eosinophilic gastritis (EoG) are two forms of eosinophilic gastrointestinal disorders (EGIDs), the incidence of which has been increasing over the past decade, including among children. These conditions are characterized by nonspecific symptoms of upper gastrointestinal tract involvement and localized eosinophilic infiltration of the mucosa. Typically, EGIDs affect only a single organ, but combined involvement may occur. The causes of such overlap remain unknown, and standardized treatment approaches have not yet been established. This article summarizes current data on the prevalence, pathogenesis, key clinical manifestations, and endoscopic and histological features of EoE and EoG, as well as contemporary therapeutic strategies. A clinical case of primary EoG is presented, illustrating the natural progressive course of the disease, culminating in the development of EoE. The effectiveness of dupilumab as biologic therapy for combined eosinophilic involvement of the stomach and esophagus is demonstrated.