Treatment of pyelonephritis in children should be combined, long-term and individual-based. The success of the therapy in children largely depends on the prompt appointment and the correct choice of antimicrobial therapy.To evaluate the efficiency of the dietary supplement "Cystenium II" in a group of children aged 7 to 14 years with a diagnosis of acute and chronic recurrent pyelonephritis in the acute phase.A total of 60 children aged 7 to 14 years with a diagnosis of acute or chronic recurrent pyelonephritis in the acute stage were included in the study. The clinical group consisted of 30 patients (mean age 12.1+/-1.8 years), while the control group included 30 patients of mean age 11.2+/-1.7 years. In the control group patients received only standard antibiotic therapy, while in the clinical group it was combined with a dietary supplement "Cystenium II" 1 tablet 2 times a day with meals for 14 days. After the course of antibacterial treatment, the children in the clinical group continued to take the studied dietary supplement for another 14 days in order to prevent the recurrence of pyelonephritis. The results of treatment (patient's condition, presence of pain, dysuria, fever) were assessed on the 3rd, 7th, 14th day, 1 and 6 months after the start of treatment. A urinalysis was performed at the baseline, on the 7th and 14th days, as well as after 1 and 6 months. Urine culture was performed before and after antibiotic therapy at the baseline, on the 14th day, 1 and 6 months after the start of treatment.The main indicators of urinalysis (leukocytes, red blood cells, protein) returned to normal values in 26 (86.7%) patients of the clinical group and in 23 (76.7%) patients of the control group on the 7th day after the start of treatment. At the completion of the basic therapy (after 14 days) normal clinical parameters (absence of leukocyturia, microhematuria, proteinuria) were observed in all patients of the clinical group and in 28 (93.3%) patients of the control group. After a month of follow-up, the disturbances in urinalysis (leukocytes, red blood cells, protein) in the control group were again seen in 3 (10%) patients, as well as after 6 months. However, in the clinical group all patients had normal urinalysis (absence of leukocyturia, microhematuria, proteinuria) after 1 month and only in 1 (3.3%) case leukocyturia, as well as an increase in the number of red blood cells and protein was detected by 6 months.According to our results, the use of dietary supplements "Cystenium II" (manufactured by Akvion, Russia), due to the constituents of D-mannose (450 mg), cranberry fruit extract with a standardized activity of 500 mg (36 mg of proanthocyanidins) and vitamin C (60 mg), may cause anti-inflammatory and anti-adhesive effects (resolving of leukocyturia and bacteriuria). This allows to use the dietary supplement Cystenium II in children from 7 years of age in the combination therapy of acute pyelonephritis, as well as exacerbation of chronic pyelonephritis. The obtained results showed a high overall therapeutic efficacy of combination therapy using Cystenium II after 6 months from the start of treatment (relapse in 1 patient), in contrast to the control group (relapse in 6 patients).the use of dietary supplement "Cystenium II" allowed to reduce the number of repeated courses of antibiotic therapy in children during 6 months of follow-up and, most likely, reduced the frequency of development of chronic pyelonephritis after an acute inflammation. Therefore, the wide clinical use of dietary supplements "Cystenium II" for the combined treatment of acute and exacerbation of chronic pyelonephritis in children older than 7 years seems to be very reasonable.