An 81-year-old man with a history of prostate cancer developed sciatica and underwent L4/5 laminectomy followed by L5/S1 transforaminal lumbar interbody fusion. Postoperatively, pain improved temporarily, then deteriorated. Tumor resection was performed after enhanced magnetic resonance imaging showed a mass distal to the left greater sciatic foramen. Histopathological examination showed the perineural spread of prostate cancer to the sciatic nerve. Developments in diagnostic imaging have revealed that prostate cancer can undergo perineural spread. Imaging studies are essential when sciatica is diagnosed in patients with a history of prostate cancer.