The objective of this study was to evaluate signal intensity increases in the greater petrosal nerve after contrast agent administration to gather information on the etiology of idiopathic peripheral facial paralysis. Magnetic resonance images were obtained from 18 patients who received inpatient medical treatment for acute peripheral facial nerve palsy. Images of intratemporal segments of the facial nerve were taken with a slice thickness of 0.75 mm. After multiplanar reconstruction, regions of interest (ROI) were defined in the proximal segment of the greater petrosal nerve. After multiplanar reconstruction, it was possible to visualize the greater petrosal nerves of all 18 patients. The nerve's average diameter was found to be 0.68 mm (range 0.5-0.9). Signal intensity increased by an average of 50.3% (range -10-146%) after contrast agent administration. Whereas this intensity was slightly reduced in two patients, it was increased in 16. No correlation could be established between greater signal intensity and medical history, clinical condition, laboratory findings, or electrophysiological data. In contrast to quantitative measurements in the facial nerve, ROI measurements in the greater petrosal nerve do not correlate with medical history, clinical condition, or laboratory findings. For this reason, MRI of this nerve does not enable us to draw conclusions on the etiology of idiopathic peripheral facial paralysis.