Material and Methods: A multi center, prospective, randomized, versus placebo, and double-blind study will be undertaken. Four-hundred patients undergoing surgery for a cerebellopontine angle tumor will be included during 23 months. Three university departments of otolaryngology (Hospital BEAUJON, CHU de Bordeaux, CHU de Tours) will participate. The pre operative assessment includes a clinical examination with the assessment of the facial function (in 6 grades according to House and BRACKMANN), an audiometry and a vestibular testing, and a cranial MRI with the classification of tumors in 4 stages according to their size. Patients will be randomized after information and with their consent. During surgery, the degree of nerve stretch (4 stages), the tumor adhesion to the nerve (4 stages) and the stimulation thresholds of the facial nerve with an electromyographic monitoring device (NIM Response 2, XOMED MEDTRONICS, Jacksonville, FL) will be recorded. All cases of facial nerve interruption during surgery will be excluded. In the treated group, one IV injection of methyl prednisolone at 1 mg/kg/day will be administered intra operatively and on postoperative days 1 and 2. The treatment will be continued on days 3 to 7 with the same dosage orally. Subsequently, 0.5 mg/kg/day at days 8 and 8, and 0.25 mg/kg/day at days 10 and 11. The facial function will be assessed on postoperative days 1, 8 and 30 clinically.