Twenty nine patients with trigeminal neuralgia were treated by retrogasserian glycerol injection method. Two of 29 were postherpetic and 27 were idiopathic trigeminal neuralgia. The mean age of these 27 was 65.2 years old ranging from 35 to 83 and the mean duration of symptoms was 7.6 years ranging from 6 months to 25 years. As previous surgical treatment there were 9 alcohol block, 5 thermorhizotomy of the Gasserian ganglion and one microvascular decompression. Twenty-two gauge needle was introduced into the trigeminal cistern via foramen ovale under the fluoroscopic control. Before injection of glycerol trigeminal cisternography using metrizamide of 300 mgI/dl was done to ascertain whether or not the needle tip was properly placed in the cistern. Patients' neck being flexed anteriorly, pure glycerol, amounting from 0.15 to 0.6 ml, was injected into the cistern with small increments through the needle. If the needle was inserted too deeply in the cistern, it is more probable that glycerol should escape from the cistern into the posterior fossa. So it was advisable that needle tip should be placed in the bottom of the cistern. When there was no pain relief, second injection was performed usually 7 days after the first injection. Complications were as follows; dysesthesia (81%), hypertension (70%), hypalgesia and hypesthesia (48%) headache (22%), ocular dysesthesia (11%), masseter weakness (7%), hyperalgesia (7%), attack of paroxysmal pain (7%). Most of these complications subsided within 8 weeks. Dysesthesia and hypalgesia that had persisted over 8 weeks were recognized in 30% of the cases.(ABSTRACT TRUNCATED AT 250 WORDS)