ABSTRACT Purpose A combination of nuclear medicine, ultrasound and voiding cystourethrography is typically used to investigate hydronephrosis in children. A major problem is the lack of an accepted gold standard to assess obstruction. In some cases the anatomy is unclear. By combining anatomical and functional information in one study, magnetic resonance imaging (MRI) has the potential of providing superior information regarding hydronephrosis. We evaluate the role of dynamic enhanced MRI and compare it to other imaging modalities in the investigation of pediatric hydronephrosis. Materials and Methods One hundred dynamic contrast enhanced MRIs were performed in 96 children (35 girls and 61 boys, mean age 4 years [range 1 month to 17 years]). The information from the various imaging modalities was compared. Results The MRI protocol was acceptable to all families and was performed without complications in all patients. The morphological imaging with MRI was superior to conventional imaging in all cases. The split renal function as calculated by nuclear and MRI scans was compared in 71 cases, and the correlation coefficient was r 2 = 0.93. The combination of ultrasound and a nuclear medicine study correlated with the final diagnosis of the MRI in 50 of 64 studies (78%). Of the 14 studies that differed 8 were obstructed on MRI but not on the nuclear studies, and 5 were not obstructed on MRI but were obstructed on the nuclear studies. One patient believed to have ureteropelvic junction obstruction on nuclear medicine scan had ureterovesical junction obstruction on MRI. The final diagnoses by MRI were ureteropelvic junction obstruction in 26 children, primary ureterovesical junction obstruction in 14, dilated but not obstructed systems in 35, duplex systems in 13, multicystic dysplastic kidneys in 5, unilateral small scarred kidney in 1, acute pyelonephritis in 2, renal mass in 1, bilateral polycystic kidneys in 1 and normal study in 9. Sedation was administered safely without any complications. Conclusions Dynamic contrast enhanced MRI provides equivalent information about renal function but superior information regarding morphology in a single study without ionizing radiation. MRI has the potential to replace the currently used combination of other imaging modalities in the investigation of hydronephrosis in children.