A specific representative of recurrent urinary tract infections (UTI) called cystitis cystica (CC) was assessed by ultrasound. The aim of the study was to delineate, by means of ultrasound measurement (US) of bladder wall thickness (BWT), the children with mere repeated UTI from those prone to frequent UTI due to CC. Two groups were compared, the control group of 30 with recurrent UTI without US CC BWT changes, and the group of 30 children with characteristic CC bladder wall thickening in whom cystoscopy was performed for verification the diagnosis of CC. BWT of > 3 mm (> 2.8 mm and > 3.3 mm) was found as cut-of value for distinction of CC versus simple recurrent UTI. US BWT measurement is useful in diagnosing CC and therefore valuable in decision about need of UTI prophylaxis.