Gas pseudocysts are a rare cause of lumbar radiculopathy and most symptomatic gas pseudocysts are found within the confines of the spinal canal. A gas pseudocyst in the foramen causing lumbar radiculopathy is very rare. We present a case of a 67-year-old woman suffering from severe pain in the right leg. Computed tomography and magnetic resonance imaging revealed a gas pseudocyst compressing the L2 root at the right L2-3 foramen. The patient underwent cyst excision using the lateral transmuscular approach and her leg pain was improved after the operation.