A case of a symptomatic spinal extradural meningeal cyst (SEMC) in Klippel-Trenaunay syndrome (KTS) is introduced. A 38-year-old woman presented with right L2 radiculopathy. She underwent operations for varicose veins in both her lower extremities. She had port-wine nevi on her trunk and extremities. The edematous change in both legs had waxed and waned. Magnetic resonance imaging showed an $11.8{ imes}13$ mm extradural meningeal cyst growing through the intervertebral foramen in L2-3. Multiple meningeal cysts were located in the dorsal aspect of the spinal cord from T3 to T10. A $5.8{ imes}6.2$ mm cyst was also found in left pleural cavity. The extradural meningeal cyst was completely excised and the preoperative symptom was improved. KTS is a congenital disorder due to a mesodermal abnormality, which may predispose the dura to weakness. The SEMC may occur through the dural defect or weakened point.