We aimed to visualize and quantify the flow of cerebrospinal fluid (CSF) across the aqueduct of Sylvius in patients with communicating hydrocephalus using phase contrast MRI, and to evaluate the effect of ventriculoperitoneal (VP) shunt surgery on flow. We investigated aqueductal CSF flow using cine cardiac-gated phase contrast MRI in 10 normal volunteers and 10 patients with communicating hydrocephalus (who underwent VP shunt surgery). For qualitative evaluation, we used an in-plane phase contrast sequence in the midsagittal plane. Quantitative through-plane measurements were performed in the axial plane perpendicular to the aqueduct. The aqueduct area ranged from 0.02 cm(2) to 0.27 cm(2) in the shunt group; and from 0.01 cm(2) to 0.04 cm(2) in the control group (p<0.05). Aqueductal stroke volume (mean, standard deviation SD) ranged from 1.9 microL to 33.17 microL (17.41 microL, 10.1132) in the control group; and from 5.63 microL to 256 microL (87.20 microL, 79.0383) in the study group. Post-operatively the aqueductal stroke volume reduced significantly, ranging from 0.60 microL to 48.77 microL (13.19 microL, 18.08) (p<0.05). Peak systolic velocity (PSV) values in the patients before shunt surgery ranged from -1.05 cm/s to -8.10 cm/s (-4.39cm/s, 2.7619) and peak diastolic velocities (PDV) ranged from 0.62 cm/s to 5.16 cm/s (3.33 cm/s, 1.4451). Post- shunt; PSV values ranged from -0.37 cm/s to -3.90 cm/s (1.78 cm/s, 1.5143) and PDV range was 0.32 cm/s to 4.43 cm/s (1.78 cm/s, 1.6782). The post-operative reduction in velocity was significant (p<0.05). Thus, the aqueductal CSF flow after VP shunt was similar to flow in healthy volunteers.