Delirium, called also "acute confusional state" is a clinical neuropsychiatry syndrome characterized by disturbance of consciousness, cognitive function, or perception, which has acute onset and fluctuating course. Delirium is hypodiagnosed in pediatric age and the data about the occurrence are insufficient and uncertained, because more than 2/3 of cases are missed. There are not studies on this ... [Show full abstract] problem in our country, where the situation is not differ from the world status. The most suitable diagnostic criteria for delirium are DSM IV criteria. They have been worked out in the adults, but there are proofs, that these criteria are applicable for children and adolescents as well. The causes, clinical characteristics and differential diagnosis of delirium are discussed in the paper. We propose a method for evaluation of acute confusional state, and suggest diagnostic and therapeutic attitude to pediatric delirium. Delirium is important, but underestimate state in children with significant morbidity and high mortality. The recognition of etiology and clinical characteristics of delirium in pediatric age will help for early diagnosis and for adequate treatment, so that not to evolve to coma and in this way will contribute to reduce the mortality rate.