Among 238 patients with bilateral trigeminal neuralgia(TN)who visited our hospital between April 2007 and June 2014, 5(2%)were surgically treated by microvascular decompression(MVD). The initial symptom was on the right side in four and on both sides in one patient. Intervals between the initial and second onset on the other side(left)were two months, and four, six, and eight years. None of the patients showed involvement of the first branch of the trigeminal nerve. The patients with bilateral TN were younger than the 154 patients with unilateral TN who were treated surgically by MVD in this period(45 vs. 65 years), and the bilateral TN patients predominantly were women(4/5 vs. 99/154). In the surgical field, the trigeminal nerve and root entry zone were compressed more by veins in the bi lateral TN patients than in the unilateral TN(4/5 vs. 60/154, respectively)patients. We could not identify any differences in MRI CISS before versus after the onset of left trigeminal neuralgia, suggesting that compression is not the sole cause of the symptom.