The aim of the present study was to evaluate the influence of previous treatment on outcome and sensory disturbance after a retrogasserian glycerol injection for trigeminal neuralgia. Ninety-nine patients with trigeminal neuralgia underwent a retrogasserian glycerol rhizotomy. Fifty-three of those patients experienced recurrent pain after the previous treatment. At the 1 year follow-up, the outcome was excellent or good in 83% of patients with no previous treatment, compared with 60 and 75% in those patients with earlier glycerol injections or radiofrequency lesions, respectively. Quantitatively assessed, the sensory impairment was most pronounced in patients who had earlier radio-frequency lesions compared with patients not treated previously. The occurrence of dysesthesia was more frequent in patients who had been surgically treated earlier. A review of the literature showed that the concentration of the glycerol preparation used probably is of great importance in terms of pain relief and sensory sequelae.