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OBJECTIVES To define the accuracy of ultrasound (US) to determine bladder volume in pediatric patients with neurogenic bladder (NB). METHODS Retrospective analysis of children with NB in treatment with urethral clean intermittent catheterization (CIC). EXCLUSION CRITERIA bladder surgeries, and catheterization through a channel different than urethra. Bladder volume was measured with ultrasound using the formula: anteroposterior bladder diameter by side to side diameter by distance from dome to outlet tract by 0.523 (cm3). In the same act, the patient was performed urethral catheterization and the drained volume was measured in millimetres. Finally, post-void residual volume (PVR) was assessed with ultrasound. RESULTS We performed 318 measurements in 299 patients, mean age was 9.95 years(SD:4.6), 59% were female. Most frequent etiologies of NB were myelomeningocele and lipomyelomeningocele. Mean ultrasound determined bladder volume was 213.9cm3 (range:20-899 cm3) and mean bladder volume drain through catheterization was 336.4ml (range:30-1480ml) (p: 0.0001). In 67.3% of the patients (n:214) PVR was not significant, and their mean ultrasound volume was 212.7 ml and the volume evacuated by catheterization was 339.9ml (p:0.0001). In all age groups ultrasound determined bladder volume was statistically lower than catheterized bladder volume (p:0.0001). The mean percentage error of the ultrasound determined bladder volume was 15.58% ± 44.09. Linear regression analysis and Bland-Altman plot showed low agreement between both measurement techniques. CONCLUSION In children with NB ultrasound determined bladder volume was statistically lower than catheterized bladder volume measured at the same moment, and this relation persisted regardless of sex, age, and the presence of PVR.