We report two cases of recurrent trigeminal neuralgia caused by an inserted prosthesis. Teflon material or polyurethane sponge inserted between the trigeminal nerve and the superior cerebellar artery became hardened and compressed the trigeminal nerve 17 months (Teflon) and 9 years (polyurethane sponge) respectively after the initial surgery. On the basis of these cases, it it suggested that actual decompression of the trigeminal nerve is important in surgery for trigeminal neuralgia, and that the prosthesis should not touch the trigeminal nerve.