The paper gives the current views of the diagnosis and treatment of Zollinger-Ellison syndrome (ZES). It underlines the importance of including ZES in differential diagnosis in patient with frequently recurrent and standard-dose proton pump inhibitor therapy-resistant erosive and ulcerative lesions of the upper gastrointestinal tract. It provides the current stepwise algorithm for the diagnosis of the pathology in question. Relevant and promising treatments in patients with ZES are considered.