Postvoid residual urine (PVR) measurement with a bladder scanning portable ultrasonographic device is an easy and non invasive method. Its use has been wide spread in men and women however its accuracy and reliability in children is still under debate. The aim of this study was to investigate the reliability of PVR measurement with real time bladder scanning in comparison with catheterization in children with voiding disorders. Postvoid residual urine measurements were routinely undertaken in patients to whom urodynamics were done, prospectively. Urinary catheterization was routinely done in all patients for cystometry. After uroflowmetry, residual urine was measured with a portable ultrasound device which readily measured the amount of PVR. After this measurement, bladder was emptied via the cystometry catheter and the drainage was noted. The age, sex and the diagnosis of the patients were also noted. The comparison between two measurements were done with paired sample t test. A total of 114 measurements were done in 89 patients. Mean age was 9±0,4 years (between 5 months to 21 years). There were 54 girls and 35 boys. The indication for urodynamics was nonneurogenic causes in 55 and neurogenic, in 34 patients. Mean PVR with ultrasonographic measurement was 56,6±6,6 ml and 56,7±7,4 ml with catheter. The difference between two measurements was statistically insignificant. Real time ultrasonographıc measurement with a bladder scanning device may be an easy, feasible, and reliable method to detect PVR in children with voiding disorders. This method may be preferred in appropriate indications like residual urine measurement in uroflowmetry+EMG studies where urinary catheterization is not necessary.