To demonstrate the possibilities of the use of oral ketamine in the treatment of postherpetic neuralgia. A pain clinic in a university hospital. A patient with postherpetic neuralgia of the ophthalmic nerve. Subcutaneous and later oral ketamine after classical treatment had failed. A complete recovery was accomplished without any sign of side effects. Oral ketamine may provide an alternative in the treatment of postherpetic neuralgia. The possible mechanism of action by its N-methyl-D-aspartate (NMDA) blocking properties is discussed.