Achondroplasia is the most common cause of congenital dwarfism and is associated with multiple complications due to impaired skeletal development. Herein, we report a 21-year-old woman with achondroplasia experiencing lower back pain which progressed to lower limb weakness and urinary retention. Magnetic resonance imaging revealed decreased interpedicular distance and severe stenosis of the lumbosacral spinal canal. Cauda equina syndrome was diagnosed and she underwent laminectomy. After decompression, pain, muscle strength and bladder function improved significantly. This case highlights the importance of early recognition of spinal compression in patients with achondroplasia.