Background: phase contrast MR imaging is a rapid, simple and non-invasive technique which is sensitive to even small CSF flows, and can be used to evaluate CSF flow both qualitatively and quantitatively. Cine phase contrast MR images show CSF flow in a dynamic, more easily appreciable, and in a more pleasing manner, allowing the delineation of obstruction, if present, along the portions of CSF pathway where obstruction is common (foramen of Monro, acqueduct of Sylvius) Patients and Methods: the study includes 20 patients from the pediatric population with ventriculomegaly (diagnosed by a radiological report) referred from Ain Shams Pediatric Hospital, Neurosurgery department at Ain Sahms University, clinic, and outpatients. Control group of 20 pediatric patients of matched age group underwent CSF flow study to obtain normal reference values. These patients had no hydrocephalus and came to our institute to undergo MRI for other neurological causes. CSF flowmetry was added to their study after obtaining oral informed consent from their parents. Results: our study included 20 patients, 8 males and 12 females, with age range 2 months - 12 years and average age 3.5 years old. All patients included were diagnosed with hydrocephalus by a previous radiological report. All patients underwent conventional MRI brain and CSF flowmetry. Patients were given diagnosis based on findings of conventional MR images, and were categorized into groups according to their underlying etiologies. 9 patients had aqueductal stenosis, 4 patients had atrophy, 2 patients had communicating hydrocephalus, 2 patients had Arnold Chiari malformation, 1 patient had Dandy-Walker variant, 1 patient had obstruction at foramen of Monro, and 1 had obstruction at foramen of Magendi. CSF flowmetry was added to evaluate the cause of hydrocephalus. Conclusion: phase contrast MR imaging is a rapid, simple and non-invasive technique which is sensitive to even small CSF flows, and can be used to evaluate CSF flow both qualitatively and quantitatively, and could be used in conjunction with conventional MRI in assessment of cases of hydrocephalus.