PURPOSE: To evaluate the clinical usefulness of 2-D Cine PC (phase contrast) technique in visualizing the pattern and the site of abnormal CSF flow and to assess the effect of a third ventriculostomy in patients with hydrocephalus. MATERIALS AND METHODS: The study group consisted of three normal controls and 13 patients with hydrocephalus, as shown on CT or MRI, and two patients who had undergone their third ventriculostomy. The technique was EKG-gated 2-D Cine PC MRI with velocity encoding 5cm/sec, TR 80msec, TE 12.3-15msec, and flip angle 15-60 degrees. Image quality was analyzed for variable sequences, and CSF flow was observed along the CSF flow pathway. We analyzed continuity and intensity of the CSF flow signal, and obstruction site and flow velocity degree were then defined. RESULTS: Systolic high and diastolic low signal intensity along the CSF flow-pathway, with normal asynchronicity and continuation, were clearly seen in normal controls. In three patients, there was obstruction at the ventricular level while others were either normal or showed a normal pattern with a weak signal. 'Normal' was defined as noncommunicating hydrocephalus and the latter as communicating hydrocephalus. In the two patients who had undergone ventriculostomy, a signal was in one case detected at the site of the third operation. CONCLUSION: A 2-D Cine PC CSF flow study enables us to see CSF flow signals noninvasively and to detect the site of obstruction of a CSF flow-pathway. It can therefore be useful for determining the application of a ventriculoperitoneal shunt and assessing the effect of a third ventriculostomy.