Introduction. Urinary tract infection is one of the most frequent bacterial infection in the development countries. Currently, the diagnosis and treatment of Acute Pyelonephritis (AP) was significantly improved. Material and methods. In the prospective study were included 196 patients with AP and a group of 22 patients with AP in pregnancy urgently admitted in the Urology Department Republican Clinical Hospital between January 1, 2017 and December 31, 2023. Results. The duration of hospitalization of urgently hospitalized patients with AP was between 3 and 28 days. Acute pyelonephritis occurs with a higher frequency in young adults, and in the case of acute pyelonephritis in pregnancy (APP), it occurs with a higher incidence in the 2nd and 3rd semester. The symptomatology of AP and APP in the groups of patients included in the study was: renal colic - lumbar pain was observed in 189 (92.6%) cases; fever in 198 (90.8%) cases; dysuria in 71(32.5%) cases; nausea 55 (25.2%) cases; vomiting in 35(16%) cases. The complications of PNA were; renal abscess 23 (10.5%) cases, acute renal carbuncle 42 (19.2%) cases, pyonephrosis 2 (0.4%) cases, paranephric abscess - 5 (2.2%) cases, toxicseptic shock - 4 (1.8%) cases. Conclusions. Acute pyelonephritis is the most serious form of urinary infection and requires hospitalization in urology or intensive care units for emergency treatment. In acute obstructive pyelonephritis, drainage of the urinary tract and prescription of large spectrum of antibiotics is crucial to prevent the development of life-threatening complications.