Eosinophilic oesophagitis is a chronic disease of the oesophagus. It is becoming more and more common and is observed to occur in both children and adults. This disease is characterized by eosinophilic infiltrations in the oesophageal mucus membrane and clinical signs of oesophageal dysfunction, such as swallowing disorders, food impaction and signs resembling refractory reflux disease. Pathogenetic mechanisms of eosinophilic oesophagitis are not known. Genetic and environmental factors are believed to be responsible. The clinical picture changes with age. In infants and young children, symptoms are non-specific, which creates a risk of overlooking the disease in differential diagnosis. School children present with abdominal pain, retrosternal pain and emesis, whereas adolescents usually report symptoms of reflux disease, dysphagia and episodes of food impaction. Dysphagia, which is rarely observed before puberty, occurs in most adults. The diagnosis of eosinophilic oesophagitis is based on clinical and histological findings. Elimination diets, local or systemic steroid therapy and endoscopic oesophageal dilation are used in treatment. Due to the chronic and recurrent nature of the disease, patients require permanent medical care, selection of appropriate and personalised steroid therapy and/or diet as well as periodical endoscopic checkups. The article presents updated information about eosinophilic oesophagitis. It discusses epidemiology, pathogenesis, clinical signs and symptoms depending on patients’ age as well as principles of diagnosis and treatment.