Perineural (Tarlov) cysts are a common benign pathology in the lumbosacral area but are rarely symptomatic, even when compressing the spinal root. Despite the rarity of Tarlov cyst formation in the foramen of the spine, this type is more symptomatic than those in other sites due to the narrow space. We introduce a biportal endoscopic fenestration for symptomatic foraminal Tarlov cysts. We present the case of a 40-year-old woman experiencing radiating pain in her right lower leg for 4 years. On seeking treatment, her great toe and ankle plantar flexion power had decreased. Magnetic resonance imaging revealed a cystic mass located in the L5-S1 intervertebral foramen that compressed the lumbar nerve root. Partial laminotomy was performed using a percutaneous biportal endoscopic system with a far lateral approach. An oval cystic mass of 2.6×1.1 cm was identified on high-definition images. Partial bone and foraminal ligament removal and cystic membrane fenestration were performed for nerve decompression. After decompression, the patient's motor weakness and radiating pain improved. Due to high-definition images and the minimally invasive laminotomy procedures associated with percutaneous biportal endoscopic fenestration, a foraminal Tarlov cyst was fenestrated safely, and weakness arising from radiculopathy was resolved in the current case. [Orthopedics. 2023;46(2):e125-e128.].