BACKGROUND: Impairment in the functions of the lower urinary tract canbe the cause of recurrent urinary tract infections (UTI) and vesicoureteral reflux (VUR) in children.The purpose of our research was to evaluate the frequency of occurrence of bladder instability in childrenwith UTI. MATERIAL/METHODS: The research involved 114 children (21 boys, 93 girls), ranging in age from5 to 16. Group I consisted of 61 children with a history of recurrent UTI, while Group II included 53children with recurrent UTI and VUR. Urodynamic tests (uroflowmetry and cystometry) were done on allthe children, while in selected cases profilometry was also performed, using a Duet apparatus (DantecMedical A/S). RESULTS: Abnormal functioning of the lower urinary tract was found in 45 children (74%)from Group I and 44 children (84%) from Group II. The most common dysfunction was instability of thedetrusor muscle, which was found in 52 children (45%), including 23 (38%) from Group I and 29 (55%) fromGroup II. In 19 children detrusor instability was accompanied by reduced bladder volume, and in 8 casesthere was a lack of detrusor-sphincter coordination. In both groups ca. 20% of the children did not presentwith symptoms indicating urination dysfunctions. Ca. 80% reported various symptoms, of which the mostcommon were nocturnal wetting and urinary urgency. In half of the children from Group I and one-fourthof the children from Group II there were several co-occurring symptoms: nocturnal and diurnal wetting,pollakiruria, and urinary urgency, or all three symptoms simultaneously. CONCLUSIONS: The most commondisturbance of lower urinary tract functioning in these children with recurrent UTI was instability ofthe detrusor muscle, which occurred more often in children with VUR.

Keywords: Adolescent, Bladder Diseases, Child, Recurrence, Urinary Tract Infections, Urodynamics, Vesico-Ureteral Reflux