Purpose: The purpose of this study is to determine the role of sonographic bladder wall thickness measurement in children with lower urinary system dysfunction. Material and methods: In this study, we reviewed 114 pediatric patients who underwent urodynamic studies for lower urinary system dysfunction between 2007-2009 at Istanbul University Cerrahpasa Medical Faculty. The patients were classified according to instable detrusor contractions and bladder wall thicknesses. Informed consent form was obtained from their parents. Results: Our study groups consisted with anatomical reasons (n=13), neurological problems (n=40) and idiopathic group (n=61). Urodynamic study detected unstable detrusor contractions in 66 patients while it did not determine contraction in 48 patients. Ultrasonography in 22 patients with unstable detrusor contraction (22/66) of bladder wall thickness was thin. In 44 patients (44/66) bladder wall thickness was detected thick. Conclusions: Our study suggests that the measurement of bladder wall thickness alone can not diagnose lower urinary system dysfunction correctly and can not replace urodynamic studies. Sonography and urodynamic studies are complementary rather than alternative modalities in evaluation and management of children with lower urinary system dysfunction.