The case of a 16-year-old boy with an aneurysmal bone cyst of the fourth lumbar vertebra and a herniated nucleus pulposus of the L4-5 disc is presented. Symptoms included progressive lower back pain and bilateral lower extremity weakness. Roentgenographic studies were consistent with a vertebral aneurysmal bone cyst with an expansile lesion that compromised the neural canal and an L4-5 herniated nucleus pulposus. Surgical treatment included tumor excision, L4-5 discectomy, lumbar decompression, and posterolateral and anterior lumbar fusion. Postoperatively, the lower back pain and lower extremity symptoms resolved. The patient continues to do well at 1-year follow-up.