Introduction. Acute pyelonephritis in children takes a leading place among the reasons for hospitalization. Objective. To study the epidemiological, anamnestic, diagnostic and clinical features of the course of pyelonephritis in children. Materials and methods. We have carried out a retrospective study of case histories of 142 children admitted to the urology department of the Emergency hospital №2 (Tomsk) with a diagnosis of acute pyelonephritis. Results. According to the results of our study, children of both sexes of young age (up to 1 year оf age) suffer from acute complicated pyelonephritis, whereas acute uncomplicated pyelonephritis is typical for girls over 3 years old. The sensitivity of ultrasound examination of the kidneys in acute pyelonephritis was 76.8%. The vast majority (96,8%) of acute uncomplicated pyelonephritis were caused by Escherichia coli. Escherichia coli was the cause of acute complicated pyelonephrities only in 30.8% of patients, Pseudomonas aeruginosa was ranked in second in frequency (15.4%), and Enteroccoccus faecalis was ranked third (11.5%). The following antibiotics retained their effectiveness among all the identified causative flora of uncomplicated pyelonephritis: fosfomycin, furagin, gentamicin, amikacin. Only amikacin showed absolute efficiency (100%) in the group of complicated pyelonephritis. 90% of bacteria showed sensitivity to fosfomycin, and 88.5% to cefepime and ertapenem. For children with acute pyelonephritis, the acute phase process of cytomegalovirus, Ebstein-Barr viral infections, previous herpes simplex virus infection, as well as contact with Chlamydia trachomatis, Ureaplasma urealуticum and Mycoplasma hominis are specific. Conclusion. The results of the study indicate the dynamics in the etiology and pathogenesis of acute pyelonephritis in children and a need for an annual monitoring in order to correct therapy.